fix export gif and add tests

Author: ikkyuland

IronSoftware.Drawing/IronSoftware.Drawing.Common.Tests/UnitTests/AnyBitmapFunctionality.cs

@@ -1083,5 +1083,30 @@ public void DW_34_ShouldNotThrowOutOfMemory(string filename)
 
             images.ForEach(bitmap => bitmap.Dispose());
         }
+
+        [FactWithAutomaticDisplayName]
+        public void AnyBitmap_ExportGif_Should_Works()
+        {
+            string imagePath = GetRelativeFilePath("van-gogh-starry-night-vincent-van-gogh.jpg");
+            var anyBitmap = AnyBitmap.FromFile(imagePath);
+
+            using var resultExport = new MemoryStream();
+            anyBitmap.ExportStream(resultExport, AnyBitmap.ImageFormat.Gif);
+            resultExport.Length.Should().NotBe(0);
+            Image.DetectFormat(resultExport.ToArray()).Should().Be(SixLabors.ImageSharp.Formats.Gif.GifFormat.Instance);
+        }
+
+        [FactWithAutomaticDisplayName]
+        public void AnyBitmap_ExportTiff_Should_Works()
+        {
+            string imagePath = GetRelativeFilePath("van-gogh-starry-night-vincent-van-gogh.jpg");
+            var anyBitmap = AnyBitmap.FromFile(imagePath);
+
+            using var resultExport = new MemoryStream();
+            anyBitmap.ExportStream(resultExport, AnyBitmap.ImageFormat.Tiff);
+            resultExport.Length.Should().NotBe(0);
+            Image.DetectFormat(resultExport.ToArray()).Should().Be(SixLabors.ImageSharp.Formats.Tiff.TiffFormat.Instance);
+        }
+
     }
 }

IronSoftware.Drawing/IronSoftware.Drawing.Common/AnyBitmap.cs

@@ -3321,11 +3321,10 @@ private static void InternalSaveAsMultiPageGif(IEnumerable<Image> images, Stream
                     // Add the correctly-sized new frame to the master GIF's frame collection.
                     gif.Frames.AddFrame(resizedFrame.Frames.RootFrame);
                 }
-
-                // Save the final result to the provided stream.
-                gif.SaveAsGif(stream);
-                stream.Position = 0;
-            }
+            }         
+            // Save the final result to the provided stream.
+            gif.SaveAsGif(stream);
+            stream.Position = 0;
         }
 
 #endregion