Re-enable DegenerateMemoryRequest test, fix Exception to be ImageFormatException

src/ImageSharp/Formats/Tga/TgaDecoder.cs

@@ -1,7 +1,9 @@
 // Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
+using System;
 using System.IO;
+using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
 
 namespace SixLabors.ImageSharp.Formats.Tga
@@ -17,7 +19,20 @@ namespace SixLabors.ImageSharp.Formats.Tga
         {
             Guard.NotNull(stream, nameof(stream));
 
-            return new TgaDecoderCore(configuration, this).Decode<TPixel>(stream);
+            var decoder = new TgaDecoderCore(configuration, this);
+
+            try
+            {
+                return decoder.Decode<TPixel>(stream);
+            }
+            catch (InvalidMemoryOperationException ex)
+            {
+                Size dims = decoder.Dimensions;
+
+                // TODO: use InvalidImageContentException here, if we decide to define it
+                // https://github.com/SixLabors/ImageSharp/issues/1110
+                throw new ImageFormatException($"Can not decode image. Failed to allocate buffers for possibly degenerate dimensions: {dims.Width}x{dims.Height}.", ex);
+            }
         }
 
         /// <inheritdoc />

src/ImageSharp/Formats/Tga/TgaDecoderCore.cs

@@ -61,6 +61,8 @@ namespace SixLabors.ImageSharp.Formats.Tga
             this.options = options;
         }
 
+        public Size Dimensions => new Size(this.fileHeader.Width, this.fileHeader.Height);
+
         /// <summary>
         /// Decodes the image from the specified stream.
         /// </summary>

tests/ImageSharp.Tests/Formats/Tga/TgaDecoderTests.cs

@@ -196,8 +196,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Tga
             }
         }
 
-        // TODO: A InvalidMemoryOperationException is thrown here, review the thrown exception.
-        [Theory(Skip = "Review Exception")]
+        [Theory]
         [WithFile(Bit16, PixelTypes.Rgba32)]
         [WithFile(Bit24, PixelTypes.Rgba32)]
         [WithFile(Bit32, PixelTypes.Rgba32)]