T79811 MacOS: Edit Mode - vertex/edge/face selection is missing

This is quite embarassing... it was returning the base instance instead of
the correct vao. No wonder that it was causing crash and at most drawing
issues.

source/blender/gpu/opengl/gl_batch.cc

@@ -249,7 +249,7 @@ GLuint GLVaoCache::base_instance_vao_get(GPUBatch *batch, int i_first)
     base_instance_ = i_first;
     GLVertArray::update_bindings(vao_base_instance_, batch, interface_, i_first);
   }
-  return base_instance_;
+  return vao_base_instance_;
 }
 
 GLuint GLVaoCache::vao_get(GPUBatch *batch)