[promises] Check if receiver is smi before loading map

BUG=v8:5343

Review-Url: https://codereview.chromium.org/2595423002
Cr-Commit-Position: refs/heads/master@{#41930}

src/builtins/builtins-promise.cc

@@ -1011,6 +1011,7 @@ TF_BUILTIN(PromiseCatch, PromiseBuiltinsAssembler) {
   Node* const context = Parameter(4);
 
   Label if_internalthen(this), if_customthen(this, Label::kDeferred);
+  GotoIf(TaggedIsSmi(promise), &if_customthen);
   BranchIfFastPath(context, promise, &if_internalthen, &if_customthen);
 
   Bind(&if_internalthen);