QScopedValueRollback: add two strategic qMove()s

Use moves instead of copies when the rhs is no longer needed
afterwards.

Change-Id: If053bfce03b886099688452ada74f6a6f36db5c2
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

src/corelib/tools/qscopedvaluerollback.h

@@ -50,12 +50,12 @@ public:
     explicit QScopedValueRollback(T &var, T value) :
         varRef(var), oldValue(var)
     {
-        varRef = value;
+        varRef = qMove(value);
     }
 
     ~QScopedValueRollback()
     {
-        varRef = oldValue;
+        varRef = qMove(oldValue);
     }
 
     void commit()