Handle invalid text correctly (#1438)

Fixes #1432

externals/skia

@@ -1 +1 @@
-Subproject commit 6df44d80ac57d857c7a954d7db24687f7e464e1c
+Subproject commit cf7362a91655c7259c35b1fecf8d892075a617d0

tests/Tests/SKPaintTest.cs

@@ -404,6 +404,17 @@ namespace SkiaSharp.Tests
 			Assert.True(paint.ContainsGlyphs(text));
 		}
 
+		[SkippableFact]
+		public void CanMeasureBadUnicodeText()
+		{
+			using var paint = new SKPaint();
+
+			var rect = SKRect.Empty;
+			var width = paint.MeasureText("\ud83c", ref rect);
+
+			Assert.Equal(0, width);
+		}
+
 		[SkippableFact]
 		public void MeasureTextMeasuresTheText()
 		{