bash_completion: fix array set checks with empty elements in them

bash_completion

@@ -335,7 +335,7 @@ __get_cword_at_cursor_by_ref()
         ((index < 0)) && index=0
     fi
 
-    local "$2" "$3" "$4" && _upvars -a${#words[@]} $2 ${words:+"${words[@]}"} \
+    local "$2" "$3" "$4" && _upvars -a${#words[@]} $2 ${words+"${words[@]}"} \
         -v $3 "$cword" -v $4 "${cur:0:index}"
 }
 
@@ -416,7 +416,7 @@ _get_comp_words_by_ref()
     }
     [[ -v vwords ]] && {
         upvars+=("$vwords")
-        upargs+=(-a${#words[@]} $vwords ${words:+"${words[@]}"})
+        upargs+=(-a${#words[@]} $vwords ${words+"${words[@]}"})
     }
 
     ((${#upvars[@]})) && local "${upvars[@]}" && _upvars "${upargs[@]}"
@@ -606,7 +606,7 @@ _filedir()
         [[ -n ${COMP_FILEDIR_FALLBACK-} && -n $arg && ${#toks[@]} -lt 1 ]] && {
             reset=$(shopt -po noglob)
             set -o noglob
-            toks+=($(compgen -f ${plusdirs:+"${plusdirs[@]}"} -- $quoted))
+            toks+=($(compgen -f ${plusdirs+"${plusdirs[@]}"} -- $quoted))
             IFS=' '
             $reset
             IFS=$'\n'