fix for crasher #75831. make sure we close the dbview when we close

the stand alone message window.  sr=bienvenu

mailnews/base/resources/content/mailWindow.js

@@ -65,6 +65,7 @@ var gIsEditableMsgFolder = false;
 function OnMailWindowUnload()
 {
   var dbview = GetDBView();
+  dump("XXX closing dbview (" + dbview + ")\n");
   if (dbview) {
     dbview.close(); 
   }

mailnews/base/resources/content/messageWindow.js

@@ -683,3 +683,7 @@ function CommandUpdate_UndoRedo()
 
 }
 
+function GetDBView()
+{
+  return gDBView;
+}