Qt: limit the size of the comboBox for network open.

It behaves badly on Win32
(cherry picked from commit 829b5a923845e3b3f6a7c57c90060410bedb47b3)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/gui/qt4/ui/open_net.ui

@@ -60,6 +60,12 @@ p > span { color: #838383; }
       </item>
       <item row="1" column="0">
        <widget class="QComboBox" name="urlComboBox">
+        <property name="maximumSize">
+         <size>
+          <width>600</width>
+          <height>16777215</height>
+         </size>
+        </property>
         <property name="editable">
          <bool>true</bool>
         </property>