Bug 1678019 - Re-add handling of lut creation failure. r=aosmond

This was found by oss-fuzz:
https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=27601
and caused by 1f9a32185f4c1d2abfe1e32d773505d865541ad7

Differential Revision: https://phabricator.services.mozilla.com/D97446

gfx/qcms/src/transform.rs

@@ -1246,6 +1246,8 @@ fn qcms_transform_precacheLUT_float(
                 (*transform).transform_fn = Some(qcms_transform_data_tetra_clut_rgb)
             }
             debug_assert!((*transform).transform_fn.is_some());
+        } else {
+            return null_mut();
         }
     }
     return Box::into_raw(transform);