fix(isql): work around nounset

Author: akinomyoga

completions/isql

@@ -6,7 +6,7 @@ _comp_cmd_isql()
     local cur prev words cword comp_args
     _comp_initialize -- "$@" || return
 
-    [[ -f $ODBCINI ]] &&
+    [[ -f ${ODBCINI-} ]] &&
         COMPREPLY=($(command grep "\[$cur" "$ODBCINI" | tr -d \[\]))
 } &&
     complete -F _comp_cmd_isql isql