do not expand button in join_groupchat_window

data/gui/join_groupchat_window.ui

@@ -235,10 +235,12 @@
                 <property name="right_attach">2</property>
                 <property name="top_attach">4</property>
                 <property name="bottom_attach">5</property>
+                <property name="y_options">GTK_EXPAND</property>
               </packing>
             </child>
           </object>
           <packing>
+            <property name="expand">False</property>
             <property name="position">0</property>
           </packing>
         </child>
@@ -317,6 +319,7 @@
           </object>
           <packing>
             <property name="expand">False</property>
+            <property name="pack_type">end</property>
             <property name="position">1</property>
           </packing>
         </child>