Fix Scanner::PushBack for surrogate code points.

A wise man once said: If you want right result, compare right value.

R=rossberg@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/1939173002
Cr-Commit-Position: refs/heads/master@{#35967}

src/parsing/scanner.h

@@ -588,7 +588,7 @@ class Scanner {
   }
 
   void PushBack(uc32 ch) {
-    if (ch > static_cast<uc32>(unibrow::Utf16::kMaxNonSurrogateCharCode)) {
+    if (c0_ > static_cast<uc32>(unibrow::Utf16::kMaxNonSurrogateCharCode)) {
       source_->PushBack(unibrow::Utf16::TrailSurrogate(c0_));
       source_->PushBack(unibrow::Utf16::LeadSurrogate(c0_));
     } else {