fix tb account manager - fallout from 222940, patch by borggraefe@web.de, r/sr=me

mail/components/prefwindow/locale/AccountManager.dtd

@@ -18,3 +18,4 @@
      XUL/FE DEVELOPERS: DO NOT MODIFY THIS VALUE. It represents the correct size of
      this window for en-US. -->
 <!ENTITY accountManager.size "width: 55em; height: 44em;"> 
+<!ENTITY accountTree.width   "width: 17em;">