Fix a crash when there is no GL context (#1328)

* Add a test for #632
* Implement checks in native code

externals/skia

@@ -1 +1 @@
-Subproject commit 4ddbe5cb84252a2896d53b80fa06584b919eb8a6
+Subproject commit 10bd203fcc03fed0ba523b6bf5dbcf3c51dbfc6b

tests/Tests/GRGlInterfaceTest.cs

@@ -7,6 +7,14 @@ namespace SkiaSharp.Tests
 {
 	public class GRGlInterfaceTest : SKTest
 	{
+		[SkippableFact]
+		public void InterfaceConstructionWithoutContextDoesNotCrash()
+		{
+			var glInterface = GRGlInterface.Create();
+
+			Assert.Null(glInterface);
+		}
+
 		[Trait(CategoryKey, GpuCategory)]
 		[SkippableFact]
 		public void CreateDefaultInterfaceIsValid()