Auto merge of #2041 - micbou:server-check-on-file-ready-to-parse, r=vheon

[READY] Do not send request in OnFileReadyToParse function if server is down

Even if `ycmd` process is terminated, YCM will try to send the `event_notification` request in `OnFileReadyToParse` function, blocking Vim for one second if the server crashed at the start (because of [this request](https://github.com/Valloric/YouCompleteMe/blob/master/python/ycm/client/base_request.py#L222)) or resulting in a traceback with  `ConnectionError` exception otherwise. This will happen for the `InsertLeave`, `CursorMoved`, `CursorHold`, `BufferVisit` events, making Vim almost unusable.

This is fixed by returning early if the process is terminated.

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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 )