FilterWidget: Fix valgrind warning about uninitialized variable.

Change-Id: I7ae99af02d5d61626eac97ddb8a6f62da9c2d638
Reviewed-by: Jarek Kobus <jaroslaw.kobus@digia.com>

src/designer/src/lib/shared/filterwidget.cpp

@@ -70,7 +70,7 @@ HintLineEdit::HintLineEdit(QWidget *parent) :
 }
 
 IconButton::IconButton(QWidget *parent)
-    : QToolButton(parent)
+    : QToolButton(parent), m_fader(1.0f)
 {
     setCursor(Qt::ArrowCursor);
 }