egl: Don't set an error when there is none

Some API will return NULL or the equivalent; sometimes it's an error,
and sometimes it's not, and the way to check that is by looking at the
return value of eglGetError(). When we check this, don't set the GError
if it returned EGL_SUCCESS, as that indicates that the return value is
expected behavior, and not an error.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2151>

src/backends/meta-egl.c

@@ -159,6 +159,9 @@ set_egl_error (GError **error)
     return;
 
   error_number = eglGetError ();
+  if (error_number == EGL_SUCCESS)
+    return;
+
   error_str = get_egl_error_str (error_number);
   g_set_error_literal (error, META_EGL_ERROR,
                        error_number,