[GSUB] Minor

src/hb-ot-layout-gsub-table.hh

@@ -920,7 +920,7 @@ struct ReverseChainSingleSubstFormat1
 			 match_coverage, this,
 			 1))
     {
-      c->buffer->cur().codepoint = substitute[index];
+      c->replace_glyph_inplace (substitute[index]);
       c->buffer->idx--; /* Reverse! */
       return TRACE_RETURN (true);
     }

src/hb-ot-layout-gsubgpos-private.hh

@@ -246,6 +246,12 @@ struct hb_apply_context_t
     set_klass_guess (klass_guess);
     buffer->replace_glyph (glyph_index);
   }
+  inline void replace_glyph_inplace (hb_codepoint_t glyph_index,
+				     unsigned int klass_guess = 0) const
+  {
+    set_klass_guess (klass_guess);
+    buffer->cur().codepoint = glyph_index;
+  }
 };