QmlDesigner: Fix infinite loop on item library resize

If item library width goes to somewhere between 50-100 pixels
(around the width of a single item), QDS gets stuck in infinite loop.
It's unclear what exactly causes this loop, as it seems to be deep
inside QtDeclarative, so worked around it by enforcing 100 pixel
minimum width for item library.

Change-Id: Ib1193cce760098edd0df61177058f134f406101e
Reviewed-by: Mahmoud Badri <mahmoud.badri@qt.io>

src/plugins/qmldesigner/components/itemlibrary/itemlibrarywidget.cpp

@@ -138,6 +138,7 @@ ItemLibraryWidget::ItemLibraryWidget(AsynchronousImageCache &imageCache,
     ItemLibraryModel::registerQmlTypes();
 
     setWindowTitle(tr("Library", "Title of library view"));
+    setMinimumWidth(100);
 
     // create header widget
     m_headerWidget->setResizeMode(QQuickWidget::SizeRootObjectToView);