Fix exception throw message for unimpl texture formats (#398)

Ryujinx.Graphics/Gal/ImageFormatConverter.cs

@@ -125,7 +125,7 @@ namespace Ryujinx.Graphics.Gal
                     break;
             }
 
-            throw new NotImplementedException("0x" + Format.ToString("x2") + " " + Type.ToString());
+            throw new NotImplementedException("0x" + ((int)Format).ToString("x2") + " " + Type.ToString());
         }
 
         public static GalImageFormat ConvertFrameBuffer(GalFrameBufferFormat Format)

Ryujinx.HLE/Gpu/Texture/TextureHelper.cs

@@ -178,7 +178,7 @@ namespace Ryujinx.HLE.Gpu.Texture
                 }
             }
 
-            throw new NotImplementedException("0x" + Image.Format.ToString("x2"));
+            throw new NotImplementedException(Image.Format.ToString());
         }
 
         public static int CompressedTextureSize(int TextureWidth, int TextureHeight, int BlockWidth, int BlockHeight, int Bpb)

Ryujinx.HLE/Gpu/Texture/TextureReader.cs

@@ -50,7 +50,7 @@ namespace Ryujinx.HLE.Gpu.Texture
                 case GalTextureFormat.Astc2D10x6:   return Read16BptCompressedTexture(Memory, Texture, 10, 6);
              }
 
-            throw new NotImplementedException("0x" + Texture.Format.ToString("x2"));
+            throw new NotImplementedException("0x" + ((int)Texture.Format).ToString("x2"));
         }
 
         private unsafe static byte[] Read1Bpp(IAMemory Memory, TextureInfo Texture)