QEasingCurve: fix mem leak in operator>>

The code ignored that the QEasingCurve passed in to op>>
might already have a QEasingCurveFunction set, overwriting
it with a new pointer without deleting the old.

Change-Id: Ic14cf7e4b97c7c8c7edb64cde08fbf22c07ac8f3
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>

src/corelib/tools/qeasingcurve.cpp

@@ -1497,6 +1497,8 @@ QDataStream &operator>>(QDataStream &stream, QEasingCurve &easing)
 
     bool hasConfig;
     stream >> hasConfig;
+    delete easing.d_ptr->config;
+    easing.d_ptr->config = Q_NULLPTR;
     if (hasConfig) {
         QEasingCurveFunction *config = curveToFunctionObject(type);
         stream >> config->_p;