Fix assertion failure when rendering mesh with degenerate transform

It isn't enough to check the top-level mesh, because attached meshes also
get a transformation from script. At least cotton branches sometimes do
that.

So check the matrix directly before using it and skip rendering.

src/graphics/C4DrawMeshGL.cpp

@@ -655,6 +655,9 @@ namespace
 			}
 		}
 
+		// Don't render with degenerate matrix
+		if (fabs(modelviewMatrix.Determinant()) < 1e-6)
+			return;
 		// Modelview matrix does not change between passes, so cache it here
 		const StdMeshMatrix normalMatrixTranspose = StdMeshMatrix::Inverse(modelviewMatrix);