Resolves: tdf#125199 format->columns dialog should be modal

Change-Id: I053dc3e8c5a5acc40e90db50c8b7d3c04feaa032
Reviewed-on: https://gerrit.libreoffice.org/72108
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

sw/uiconfig/swriter/ui/columndialog.ui

 <?xml version="1.0" encoding="UTF-8"?>
-<!-- Generated with glade 3.18.3 -->
+<!-- Generated with glade 3.22.1 -->
 <interface domain="sw">
   <requires lib="gtk+" version="3.18"/>
   <object class="GtkDialog" id="ColumnDialog">
@@ -7,7 +7,11 @@
     <property name="border_width">6</property>
     <property name="title" translatable="yes" context="columndialog|ColumnDialog">Columns</property>
     <property name="resizable">False</property>
+    <property name="modal">True</property>
     <property name="type_hint">dialog</property>
+    <child>
+      <placeholder/>
+    </child>
     <child internal-child="vbox">
       <object class="GtkBox" id="dialog-vbox1">
         <property name="can_focus">False</property>