fix(webgl): fix issue https://github.com/servo/servo/issues/21352

If we have a bounded framebuffer previously, which is not the one to delete.
we would not change the !binding, but we would change the GLSide with Command::BindFramebuffer(Default).

components/script/dom/webglrenderingcontext.rs

@@ -93,12 +93,11 @@ macro_rules! handle_object_deletion {
         if let Some(bound_object) = $binding.get() {
             if bound_object.id() == $object.id() {
                 $binding.set(None);
-            }
-
                 if let Some(command) = $unbind_command {
                     $self_.send_command(command);
                 }
             }
+        }
     };
 }