fix for issues #10259 and #19978

#10259
qdesigner_propertysheet.cpp:  method metaProperty(int index)
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qdesigner_internal::PropertySheetEnumValue pse = qdesigner_internal::PropertySheetEnumValue(v.toInt(), designerMetaEnumFor(p->enumerator()));
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v.toInt() conversion is wrong since QVariant<Qt::FucusPolicy> declared as user metatype in qtsetup.cpp and have no rules for convert it to integer.

#19978
trying to access to "_designer" pointer after object has been destoyed;