fix(python): nounset mode error with no -X completions

Author: scop

completions/python

@@ -48,7 +48,7 @@ _python()
                 awk '$1 == "-X" && $2 ~ /:$/ {
                     sub(":$","",$2); sub("=.*","=",$2); print $2
                 }')" -- "$cur"))
-            [[ $COMPREPLY == *= ]] && compopt -o nospace
+            [[ ${COMPREPLY-} == *= ]] && compopt -o nospace
             return
             ;;
         --jit)