patch 8.2.3977: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more error messages to errors.h.
diff --git a/src/clientserver.c b/src/clientserver.c
index 2fefcc4..ca6a4eb 100644
--- a/src/clientserver.c
+++ b/src/clientserver.c
@@ -929,7 +929,7 @@
 		|| serverReadReply(X_DISPLAY, serverStrToWin(serverid),
 						       &r, FALSE, timeout) < 0)
 # endif
-	    emsg(_("E277: Unable to read a server reply"));
+	    emsg(_(e_unable_to_read_server_reply));
     }
 #endif
     rettv->v_type = VAR_STRING;