Avoid using defaults, because of issue with netcore2.1 in Release mode

src/ImageSharp/Formats/Tiff/PhotometricInterpretation/BlackIsZero16TiffColor{TPixel}.cs

@@ -25,11 +25,13 @@ namespace SixLabors.ImageSharp.Formats.Tiff.PhotometricInterpretation
         /// <inheritdoc/>
         public override void Decode(ReadOnlySpan<byte> data, Buffer2D<TPixel> pixels, int left, int top, int width, int height)
         {
+            // Note: due to an issue with netcore 2.1 and default values and unpredictable behavior with those,
+            // we define our own defaults as a workaround. See: https://github.com/dotnet/runtime/issues/55623
+            L16 l16 = TiffUtils.L16Default;
             var color = default(TPixel);
+            color.FromVector4(TiffUtils.Vector4Default);
 
             int offset = 0;
-
-            var l16 = default(L16);
             for (int y = top; y < top + height; y++)
             {
                 Span<TPixel> pixelRow = pixels.GetRowSpan(y);

src/ImageSharp/Formats/Tiff/PhotometricInterpretation/Rgb161616TiffColor{TPixel}.cs

@@ -25,11 +25,14 @@ namespace SixLabors.ImageSharp.Formats.Tiff.PhotometricInterpretation
         /// <inheritdoc/>
         public override void Decode(ReadOnlySpan<byte> data, Buffer2D<TPixel> pixels, int left, int top, int width, int height)
         {
+            // Note: due to an issue with netcore 2.1 and default values and unpredictable behavior with those,
+            // we define our own defaults as a workaround. See: https://github.com/dotnet/runtime/issues/55623
+            Rgba64 rgba = TiffUtils.Rgba64Default;
             var color = default(TPixel);
+            color.FromVector4(TiffUtils.Vector4Default);
 
             int offset = 0;
 
-            var rgba = default(Rgba64);
             for (int y = top; y < top + height; y++)
             {
                 Span<TPixel> pixelRow = pixels.GetRowSpan(y);

src/ImageSharp/Formats/Tiff/PhotometricInterpretation/Rgb16PlanarTiffColor{TPixel}.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System.Buffers;
+using System.Numerics;
 using SixLabors.ImageSharp.Formats.Tiff.Utils;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
@@ -25,14 +26,17 @@ namespace SixLabors.ImageSharp.Formats.Tiff.PhotometricInterpretation
         /// <inheritdoc/>
         public override void Decode(IMemoryOwner<byte>[] data, Buffer2D<TPixel> pixels, int left, int top, int width, int height)
         {
+            // Note: due to an issue with netcore 2.1 and default values and unpredictable behavior with those,
+            // we define our own defaults as a workaround. See: https://github.com/dotnet/runtime/issues/55623
+            Rgba64 rgba = TiffUtils.Rgba64Default;
             var color = default(TPixel);
+            color.FromVector4(TiffUtils.Vector4Default);
 
             System.Span<byte> redData = data[0].GetSpan();
             System.Span<byte> greenData = data[1].GetSpan();
             System.Span<byte> blueData = data[2].GetSpan();
 
             int offset = 0;
-            var rgba = default(Rgba64);
             for (int y = top; y < top + height; y++)
             {
                 System.Span<TPixel> pixelRow = pixels.GetRowSpan(y);

src/ImageSharp/Formats/Tiff/PhotometricInterpretation/WhiteIsZero16TiffColor{TPixel}.cs

@@ -25,11 +25,13 @@ namespace SixLabors.ImageSharp.Formats.Tiff.PhotometricInterpretation
         /// <inheritdoc/>
         public override void Decode(ReadOnlySpan<byte> data, Buffer2D<TPixel> pixels, int left, int top, int width, int height)
         {
+            // Note: due to an issue with netcore 2.1 and default values and unpredictable behavior with those,
+            // we define our own defaults as a workaround. See: https://github.com/dotnet/runtime/issues/55623
+            L16 l16 = TiffUtils.L16Default;
             var color = default(TPixel);
+            color.FromVector4(TiffUtils.Vector4Default);
 
             int offset = 0;
-
-            var l16 = default(L16);
             for (int y = top; y < top + height; y++)
             {
                 Span<TPixel> pixelRow = pixels.GetRowSpan(y);

src/ImageSharp/Formats/Tiff/Utils/TiffUtils.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Buffers.Binary;
+using System.Numerics;
 using System.Runtime.CompilerServices;
 using SixLabors.ImageSharp.PixelFormats;
 
@@ -13,6 +14,12 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Utils
     /// </summary>
     internal static class TiffUtils
     {
+        public static Vector4 Vector4Default { get; } = new Vector4(0.0f, 0.0f, 0.0f, 0.0f);
+
+        public static Rgba64 Rgba64Default { get; } = new Rgba64(0, 0, 0, 0);
+
+        public static L16 L16Default { get; } = new L16(0);
+
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static ushort ConvertToShortBigEndian(ReadOnlySpan<byte> buffer) =>
             BinaryPrimitives.ReadUInt16BigEndian(buffer);