Add test for malformed SVG path parsing

Author: JimBobSquarePants

src/ImageSharp.Drawing/Path.cs

@@ -575,6 +575,7 @@ private static bool TryFindFlag(ref ReadOnlySpan<char> str, out bool value)
 
         // https://www.w3.org/TR/SVG11/paths.html#PathDataBNF
         // flag: "0" | "1"
+        // Adjacent flags are valid, so this consumes exactly one character.
         if (str.Length == 0 || (str[0] is not '0' and not '1'))
         {
             value = default;

tests/ImageSharp.Drawing.Tests/Shapes/PathTests.cs

@@ -86,6 +86,34 @@ public void EmptyPath_ToLinearGeometry_ReturnsEmptyGeometry()
         Assert.False(segments.MoveNext());
     }
 
+    [Theory]
+    [InlineData("M")]
+    [InlineData("M 5")]
+    [InlineData("V")]
+    [InlineData("H")]
+    [InlineData("C 1 2")]
+    [InlineData("S 6 7")]
+    [InlineData("Q 3 4 5")]
+    [InlineData("T")]
+    [InlineData("A 1 2 3 4 5 6")]
+    [InlineData("~ 7 6 5")]
+    public void TryParseSvgPath_ReturnsFalseForMalformedPathData(string svgPath)
+        => Assert.False(Path.TryParseSvgPath(svgPath, out _));
+
+    [Theory]
+    [InlineData("M 10 10 L 1e999 20")]
+    [InlineData("M 10 10 L NaN 20")]
+    [InlineData("M 10 10 L Infinity 20")]
+    [InlineData("M 10 10 h 1e999")]
+    [InlineData("M 10 10 v 1e999")]
+    [InlineData("M 10 10 A 25 25 0 2 0 50 50")]
+    [InlineData("M 10 10 A 25 25 0 0 2 50 50")]
+    [InlineData("M 10 10 L")]
+    [InlineData("M 10 10 Q 20 20")]
+    [InlineData("M 10 10 C 20 20 30 30")]
+    public void TryParseSvgPath_ReturnsFalseForInvalidPathDataBoundaries(string svgPath)
+        => Assert.False(Path.TryParseSvgPath(svgPath, out _));
+
     [Fact]
     public void PathCollection_EnumerableConstructor_PreservesPaths()
     {