Added a test for interface impls not added if the interface has already been created.

Signed-off-by: Dimitar Dobrev <dpldobrev@yahoo.com>

tests/CSharpTemp/CSharpTemp.Tests.cs

@@ -14,6 +14,14 @@ public class CSharpTempTests : GeneratorTestFixture
         }
     }
 
+    [Test]
+    public void TestIncompilableCode()
+    {
+        using (new ForceCreationOfInterface())
+        {
+        }
+    }
+
     [Test]
     public void TestIndexer()
     {

tests/CSharpTemp/CSharpTemp.h

@@ -68,6 +68,10 @@ private:
 
 Bar::Bar() {}
 
+class DLL_API ForceCreationOfInterface : public Foo, public Bar
+{
+};
+
 class DLL_API Baz : public Foo, public Bar
 {
 public: