fish: Optimize description alignment of completions (#4912)

Close #4910

shell/completion.fish

@@ -124,10 +124,8 @@ function fzf_complete -w fzf -d 'fzf command completion and wildcard expansion s
 
       # Determine the tabstop length for description alignment
       set -l -- max_columns (math $COLUMNS - 40)
-      for i in $list[1..500]
-        set -l -- item (string split -f 1 -- \t $i)
-        and set -l -- len (string length -V -- $item)
-        and test "$len" -gt "$tabstop" -a "$len" -lt "$max_columns"
+      for len in (string match -r -- '^[^\\t]*(?=\\t)' $list[1..500] | string length -V)
+        test "$len" -gt "$tabstop" -a "$len" -lt "$max_columns"
         and set -- tabstop $len
       end
       set -- tabstop (math $tabstop + 4)