fix crash when GetFontMetrics() returns nil, which should never happen of course

webshell/src/nsThrobber.cpp

@@ -238,11 +238,14 @@ HandleThrobberEvent(nsGUIEvent *aEvent)
         cx->SetColor(NS_RGB(255, 255, 255));
         cx->SetFont(tfont);
         met = cx->GetFontMetrics();
+        if (nsnull != met)
+        {
           met->GetWidth(str, w);
           met->GetHeight(h);
           cx->DrawString(str, 2, (bounds.width - w) >> 1, (bounds.height - h) >> 1, 0);
           NS_RELEASE(met);
         }
+      }
       else
       {
         cx->DrawImage(img, 1, 1);