[PATCH] fix _gdb shift error

[tiandic <2323748675@xxxxxx>]

This error is triggered when using `gdb -cd <TAB>`
---
 Completion/Unix/Command/_gdb | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Completion/Unix/Command/_gdb b/Completion/Unix/Command/_gdb
index 6bdd55946..7470e6102 100644
--- a/Completion/Unix/Command/_gdb
+++ b/Completion/Unix/Command/_gdb
@@ -43,7 +43,7 @@ else
   w=( "${(@)words[2,CURRENT-1]}" )
   while [[ "$w[1]" = -* ]]; do
     [[ "$w[1]" = -(cd|se|tty|[decsxb]) ]] && shift 1 w
-    shift 1 w
+    (( $#w )) && shift 1 w
   done
 
   if [[ $#w -gt 1 ]]; then
-- 
2.56.0