SL-12888 Fix space alpha megaprim not using z-test

indra/newview/llvowlsky.cpp

@@ -301,6 +301,8 @@ void LLVOWLSky::drawDome(void)
 		updateGeometry(mDrawable);
 	}
 
+	LLGLDepthTest gls_depth(GL_TRUE, GL_FALSE);
+
 	const U32 data_mask = LLDrawPoolWLSky::SKY_VERTEX_DATA_MASK;
 	
 	std::vector< LLPointer<LLVertexBuffer> >::const_iterator strips_vbo_iter, end_strips;