patch 8.2.3967: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more errors to errors.h.
diff --git a/src/gui_x11.c b/src/gui_x11.c
index 2e87177..07699d3 100644
--- a/src/gui_x11.c
+++ b/src/gui_x11.c
@@ -1218,7 +1218,7 @@
     if (app_context == NULL || gui.dpy == NULL)
     {
 	gui.dying = TRUE;
-	emsg(_(e_opendisp));
+	emsg(_(e_cannot_open_display));
 	return FAIL;
     }
     return OK;