Do not send request if server is down

Do not send an "event_notification" request in OnFileReadyToParse
function if server process is terminated. Otherwise, it blocks Vim
for one second or results in a traceback each time the InsertLeave,
CursorMoved, CursorHold, and BufferVisit events are triggered.

python/ycm/youcompleteme.py

@@ -256,10 +256,11 @@ class YouCompleteMe( object ):
 
 
   def OnFileReadyToParse( self ):
-    self._omnicomp.OnFileReadyToParse( None )
-
     if not self.IsServerAlive():
       self._NotifyUserIfServerCrashed()
+      return
+
+    self._omnicomp.OnFileReadyToParse( None )
 
     extra_data = {}
     self._AddTagsFilesIfNeeded( extra_data )