work around a bug in zsh that percent-expands `%1F{2}` as if it was `%F{2}`; fixes #270

internal/p10k.zsh

@@ -444,11 +444,10 @@ _p9k_background() {
 }
 
 _p9k_foreground() {
-  case $1 in
-    '')   _p9k_ret="%f";;
-    '#'*) _p9k_ret="%F{$1}";;
-    *)    _p9k_ret="%${1}F";;
-  esac
+  # Note: This code used to produce `%1F` instead of `%F{1}` because it's more efficient.
+  # Unfortunately, this triggers a bug in zsh. Namely, `%1F{2}` gets percent-expanded as if
+  # it was `%F{2}`.
+  [[ -n $1 ]] && _p9k_ret="%F{$1}" || _p9k_ret="%k"
 }
 
 _p9k_escape_style() {