QWindowsVistaStyle: Set theme flag noContent for PE_FrameLineEdit

When the flag is not set, custom background colors for QLineEdit
will not work. Set the flag as does QWindowsXpStyle.

Task-number: QTBUG-57862
Change-Id: I6e653c2cdc8cc523673e1629bf42f833c8504431
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>

src/widgets/styles/qwindowsvistastyle.cpp

@@ -600,6 +600,7 @@ void QWindowsVistaStyle::drawPrimitive(PrimitiveElement element, const QStyleOpt
                 XPThemeData theme(widget, painter,
                                   QWindowsXPStylePrivate::EditTheme,
                                   EP_EDITBORDER_NOSCROLL, stateId, option->rect);
+                theme.noContent = true;
                 painter->save();
                 QRegion clipRegion = option->rect;
                 clipRegion -= option->rect.adjusted(2, 2, -2, -2);