Fix truncation warning in generation_helpers

Remove redundant if-statement and return bool value, rather than -1.

Fixes: QTBUG-122302
Change-Id: I06e98eb76e160f7dd7859ab43f23eb3b6540dbd5
Reviewed-by: Matthias Rauter <matthias.rauter@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

tests/auto/concurrent/qtconcurrentfiltermapgenerated/generation_helpers.h

@@ -131,10 +131,7 @@ public:
 
     bool operator()(const T &el)
     {
-        if (!movedFrom)
-            return el.isOdd();
-        else
-            return -1;
+        return movedFrom || el.isOdd();
     }
 };