C++: Do not insert matching } within string

Regression from

    commit a6aa287720
    C++: Fine-tune auto insertion of '}'

Change-Id: I3ede8c7a1e3c73708d5d5a59c314e4b4596976b2
Reviewed-by: Ivan Donchevskii <ivan.donchevskii@qt.io>
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/libs/cplusplus/MatchingText.cpp

@@ -326,6 +326,11 @@ static bool allowAutoClosingBrace(const QTextCursor &cursor,
 
     int prevState;
     const Tokens tokens = getTokens(cursor, prevState);
+
+    const Token token = tokenAtPosition(tokens, cursor.positionInBlock());
+    if (token.isStringLiteral())
+        return false;
+
     if (isAfterNamespaceDefinition(tokens, cursor.positionInBlock()))
         return false;