[ReverseChainSingleSubst] Minor optimization

src/OT/Layout/GSUB/ReverseChainSingleSubstFormat1.hh

@@ -109,12 +109,12 @@ struct ReverseChainSingleSubstFormat1
   bool apply (hb_ot_apply_context_t *c) const
   {
     TRACE_APPLY (this);
-    if (unlikely (c->nesting_level_left != HB_MAX_NESTING_LEVEL))
-      return_trace (false); /* No chaining to this type */
-
     unsigned int index = (this+coverage).get_coverage (c->buffer->cur ().codepoint);
     if (likely (index == NOT_COVERED)) return_trace (false);
 
+    if (unlikely (c->nesting_level_left != HB_MAX_NESTING_LEVEL))
+      return_trace (false); /* No chaining to this type */
+
     const auto &lookahead = StructAfter<decltype (lookaheadX)> (backtrack);
     const auto &substitute = StructAfter<decltype (substituteX)> (lookahead);