fix non-global s///

QString::replace(QRegExp) pretty much always detaches, so the equality
check was bogus.

Change-Id: Iee9043c1ee3083edaf289886ac11b3e3a501d623
Reviewed-by: Daniel Teske <daniel.teske@nokia.com>

src/shared/proparser/qmakeevaluator.cpp

@@ -329,7 +329,7 @@ static void replaceInList(ProStringList *varlist,
         QString val = varit->toQString(tmp);
         QString copy = val; // Force detach and have a reference value
         val.replace(regexp, replace);
-        if (!val.isSharedWith(copy)) {
+        if (!val.isSharedWith(copy) && val != copy) {
             if (val.isEmpty()) {
                 varit = varlist->erase(varit);
             } else {