patch 8.2.0614: get ml_get error when deleting a line in 'completefunc'

Problem:    Get ml_get error when deleting a line in 'completefunc'. (Yegappan
            Lakshmanan)
Solution:   Lock the text while evaluating 'completefunc'.

src/ex_getln.c

@@ -2576,7 +2576,7 @@ get_text_locked_msg(void)
     if (cmdwin_type != 0)
 	return e_cmdwin;
 #endif
-    return e_secure;
+    return e_textlock;
 }
 
 /*