Fix missing cases of empty_string canonicalization

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 41c3edc707095d860703378924a2ce85d83ea7c4..b53d167e5461d5abe5caa0844a84d6b27ca82f21 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -11708,6 +11708,9 @@ bool String::SlowAsArrayIndex(uint32_t* index) {
 
 
 Handle<String> SeqString::Truncate(Handle<SeqString> string, int new_length) {
+  Heap* heap = string->GetHeap();
+  if (new_length == 0) return heap->isolate()->factory()->empty_string();
+
   int new_size, old_size;
   int old_length = string->length();
   if (old_length <= new_length) return string;
@@ -11727,7 +11730,6 @@ Handle<String> SeqString::Truncate(Handle<SeqString> string, int new_length) {
   DCHECK_OBJECT_ALIGNED(start_of_string);
   DCHECK_OBJECT_ALIGNED(start_of_string + new_size);
 
-  Heap* heap = string->GetHeap();
   // Sizes are pointer size aligned, so that we can use filler objects
   // that are a multiple of pointer size.
   heap->CreateFillerObjectAt(start_of_string + new_size, delta,
@@ -11738,7 +11740,6 @@ Handle<String> SeqString::Truncate(Handle<SeqString> string, int new_length) {
   // for the left-over space to avoid races with the sweeper thread.
   string->synchronized_set_length(new_length);
 
-  if (new_length == 0) return heap->isolate()->factory()->empty_string();
   return string;
 }