Fix loop bounds for little endian, add little endian test file

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

@@ -53,7 +53,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff.PhotometricInterpretation
                 }
                 else
                 {
-                    for (int x = left; x < left + width; x++)
+                    for (int x = 0; x < pixelRow.Length; x++)
                     {
                         ulong r = TiffUtils.ConvertToShortLittleEndian(data.Slice(offset, 2));
                         offset += 2;

tests/ImageSharp.Tests/Formats/Tiff/TiffDecoderTests.cs

@@ -165,6 +165,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Tiff
 
         [Theory]
         [WithFile(FlowerRgb161616Contiguous, PixelTypes.Rgba32)]
+        [WithFile(FlowerRgb161616ContiguousLittleEndian, PixelTypes.Rgba32)]
         [WithFile(FlowerRgb161616Planar, PixelTypes.Rgba32)]
         [WithFile(FlowerRgb161616PlanarLittleEndian, PixelTypes.Rgba32)]
         [WithFile(Issues1716Rgb161616BitLittleEndian, PixelTypes.Rgba32)]

tests/ImageSharp.Tests/TestImages.cs

@@ -562,6 +562,7 @@ namespace SixLabors.ImageSharp.Tests
             public const string Rgb4BitPalette = "Tiff/bike_colorpalette_4bit.tiff";
             public const string RgbPaletteDeflate = "Tiff/rgb_palette_deflate.tiff";
             public const string FlowerRgb161616Contiguous = "Tiff/flower-rgb-contig-16.tiff";
+            public const string FlowerRgb161616ContiguousLittleEndian = "Tiff/flower-rgb-contig-16_lsb.tiff";
             public const string FlowerRgb161616Planar = "Tiff/flower-rgb-planar-16.tiff";
             public const string FlowerRgb161616PlanarLittleEndian = "Tiff/flower-rgb-planar-16_lsb.tiff";
             public const string FlowerRgb141414Contiguous = "Tiff/flower-rgb-contig-14.tiff";

tests/Images/Input/Tiff/flower-rgb-contig-16_lsb.tiff

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:0951a9c2207eb6864b6a19ec8513a28a874adddb37c3c06b9fd07831372924e3
+size 19150