fix(_comp_delimited): nounset mode error on first token

Author: scop

bash_completion

@@ -708,7 +708,7 @@ _comp_delimited()
         existing=($cur)
         # Do not remove the last from existing if it's not followed by the
         # delimiter so we get space appended.
-        [[ $cur == *"$delimiter" ]] || unset "existing[${#existing[@]}-1]"
+        [[ ! $cur || $cur == *"$delimiter" ]] || unset "existing[${#existing[@]}-1]"
         IFS=$ifs
         for x in ${existing+"${existing[@]}"}; do
             for i in "${!COMPREPLY[@]}"; do