[scanner] Fix string scanning corner-case

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No-Tree-Checks: true
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Change-Id: I287197c8603e9e550d7f4832c1f85009136f4bb0
Reviewed-on: https://chromium-review.googlesource.com/c/1329961
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57407}

src/parsing/scanner.cc

@@ -548,6 +548,7 @@ Token::Value Scanner::ScanString() {
 
   LiteralScope literal(this);
   while (true) {
+    if (V8_UNLIKELY(c0_ == kEndOfInput)) return Token::ILLEGAL;
     if ((V8_UNLIKELY(static_cast<uint32_t>(c0_) >= kMaxAscii) &&
          !unibrow::IsStringLiteralLineTerminator(c0_)) ||
         !MayTerminateString(character_scan_flags[c0_])) {