Fix PngMetadata copy

Author: SpaceCheetah

src/ImageSharp/Formats/Png/PngMetadata.cs

@@ -29,6 +29,7 @@ private PngMetadata(PngMetadata other)
         this.InterlaceMethod = other.InterlaceMethod;
         this.TransparentColor = other.TransparentColor;
         this.RepeatCount = other.RepeatCount;
+        this.DefaultImageAnimated = other.DefaultImageAnimated;
 
         if (other.ColorTable?.Length > 0)
         {
@@ -86,7 +87,7 @@ private PngMetadata(PngMetadata other)
     /// <summary>
     ///  Gets or sets a value indicating whether the default image is shown as part of the animated sequence
     /// </summary>
-    public bool DefaultImageAnimated { get; set; }
+    public bool DefaultImageAnimated { get; set; } = true;
 
     /// <inheritdoc/>
     public IDeepCloneable DeepClone() => new PngMetadata(this);

tests/ImageSharp.Tests/Formats/Png/PngMetadataTests.cs

@@ -32,7 +32,8 @@ public void CloneIsDeep()
             InterlaceMethod = PngInterlaceMode.Adam7,
             Gamma = 2,
             TextData = new List<PngTextData> { new PngTextData("name", "value", "foo", "bar") },
-            RepeatCount = 123
+            RepeatCount = 123,
+            DefaultImageAnimated = false
         };
 
         PngMetadata clone = (PngMetadata)meta.DeepClone();
@@ -44,6 +45,7 @@ public void CloneIsDeep()
         Assert.False(meta.TextData.Equals(clone.TextData));
         Assert.True(meta.TextData.SequenceEqual(clone.TextData));
         Assert.True(meta.RepeatCount == clone.RepeatCount);
+        Assert.True(meta.DefaultImageAnimated == clone.DefaultImageAnimated);
 
         clone.BitDepth = PngBitDepth.Bit2;
         clone.ColorType = PngColorType.Palette;