Prevent read-after-buffer in SourcePositionTableIterator::Advance.

R=yangguo@chromium.org
BUG=chromium:667142

Review-Url: https://codereview.chromium.org/2525663003
Cr-Commit-Position: refs/heads/master@{#41224}

src/source-position-table.cc

@@ -175,7 +175,7 @@ SourcePositionTableIterator::SourcePositionTableIterator(ByteArray* byte_array)
 void SourcePositionTableIterator::Advance() {
   DCHECK(!done());
   DCHECK(index_ >= 0 && index_ <= table_->length());
-  if (index_ == table_->length()) {
+  if (index_ >= table_->length()) {
     index_ = kDone;
   } else {
     PositionTableEntry tmp;