Parse: An empty escaped identifier is entirely whitespace

Author: slavapestov

lib/Parse/Lexer.cpp

@@ -661,7 +661,7 @@ static bool advanceIfValidContinuationOfOperator(char const *&ptr,
 /// Returns true if the given string is entirely whitespace (considering only
 /// those whitespace code points permitted in raw identifiers).
 static bool isEntirelyWhitespace(StringRef string) {
-  if (string.empty()) return false;
+  if (string.empty()) return true;
   char const *p = string.data(), *end = string.end();
   if (!advanceIf(p, end, isPermittedRawIdentifierWhitespace))
     return false;