'main': Optimize the path_prefix check.

Computing ${#array} is O(N), whereas checking 0 is O(1).

highlighters/main/main-highlighter.zsh

@@ -1117,9 +1117,10 @@ _zsh_highlight_main_highlighter_check_path()
   # If this word ends the buffer, check if it's the prefix of a valid path.
   if (( has_end && (len == end_pos) )) &&
      [[ $WIDGET != zle-line-finish ]]; then
+    # TODO: When we've dropped support for pre-5.0.6 zsh, use the *(Y1) glob qualifier here.
     local -a tmp
     tmp=( ${expanded_path}*(N) )
-    (( $#tmp > 0 )) && REPLY=path_prefix && return 0
+    (( ${+tmp[1]} )) && REPLY=path_prefix && return 0
   fi
 
   # It's not a path.