Bail out of loads if were going away. Bug 369126, r+sr=jst

docshell/base/nsDocShell.cpp

@@ -6257,6 +6257,8 @@ nsDocShell::InternalLoad(nsIURI * aURI,
 
     NS_ENSURE_TRUE(IsValidLoadType(aLoadType), NS_ERROR_INVALID_ARG);
 
+    NS_ENSURE_TRUE(!mIsBeingDestroyed, NS_ERROR_NOT_AVAILABLE);
+
     // wyciwyg urls can only be loaded through history. Any normal load of
     // wyciwyg through docshell is  illegal. Disallow such loads.
     if (aLoadType & LOAD_CMD_NORMAL) {