fix: omit :foreground from emoji icon face when no color provided

The font branch of wttrin--make-emoji-icon built its face plist with `:foreground foreground` even when foreground was nil, producing a literal `(:family ... :height 1.0 :foreground nil)`. The mode-line redisplays many times per second, and Emacs validates faces on every redisplay. A single fresh-cache state produced hundreds of "Invalid face attribute :foreground nil" warnings in *Messages*. The bug's been live since 2026-02-21 (b74b98f). The 130bbc07 helper extraction kept it in place.

Switch to backquote splicing so the :foreground key is included only when foreground is non-nil. Behavior is identical on the colored path. On the nil path the emoji renders with the default mode-line color, the same visible result as before, without the warning flood.

1 files changed, 7 insertions, 4 deletions

diff --git a/wttrin.el b/wttrin.el
index d09a64a..0f84f7a 100644
--- a/wttrin.el
+++ b/wttrin.el
@@ -597,12 +597,15 @@ user's original casing so tooltips display what the user expects."
 
 (defun wttrin--make-emoji-icon (emoji &optional foreground)
   "Create EMOJI string with optional font face and FOREGROUND color.
-Uses `wttrin-mode-line-emoji-font' when configured."
+Uses `wttrin-mode-line-emoji-font' when configured.
+Omits `:foreground' from the face plist when FOREGROUND is nil — a literal
+`:foreground nil' entry triggers \"Invalid face attribute\" warnings on every
+redisplay."
   (if wttrin-mode-line-emoji-font
       (propertize emoji
-                  'face (list :family wttrin-mode-line-emoji-font
-                              :height 1.0
-                              :foreground foreground))
+                  'face `(:family ,wttrin-mode-line-emoji-font
+                          :height 1.0
+                          ,@(when foreground (list :foreground foreground))))
     (if foreground
         (propertize emoji 'face (list :foreground foreground))
       emoji)))