QProxyStyle: fix the base style assignment in constructor

Assign the baseStyle member before calling setParent(), because that
will trigger ParentChange event and thus calls ensureBaseStyle(). The
baseStyle member must be set at that point, because otherwise it will
start creating a fallback base style.

Change-Id: I3522e41bb6b82e3fe2e7790d53a53978c18a027a
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>

src/widgets/styles/qproxystyle.cpp

@@ -120,9 +120,9 @@ QProxyStyle::QProxyStyle(QStyle *style) :
 {
     Q_D(QProxyStyle);
     if (style) {
+        d->baseStyle = style;
         style->setProxy(this);
         style->setParent(this); // Take ownership
-        d->baseStyle = style;
     }
 }