CPlusPlus: Fix isQtReservedWord

checking for size >= 4 masks Q_D and Q_Q.

Change-Id: If9ab7d3b2c2c571e73b98e89908e492fc6241296
Reviewed-by: Erik Verbruggen <erik.verbruggen@qt.io>

src/libs/cplusplus/pp-engine.cpp

@@ -89,7 +89,7 @@ static bool same(const char *a, const char *b, int size)
 
 static bool isQtReservedWord(const char *name, int size)
 {
-    if (size < 4)
+    if (size < 3)
         return false;
 
     const char c = name[0];