ActiveModColor: Cache the list of modifiers at setup time too

In order for the plugin to work without having to switch layers once, it needs
to scan the keymap for modifiers at setup time too. We do this by calling
`onLayerChange()`, which already does that.

Fixes #670.

Signed-off-by: Gergely Nagy <algernon@keyboard.io>

src/kaleidoscope/plugin/LED-ActiveModColor.h

@@ -37,6 +37,9 @@ class ActiveModColorEffect : public kaleidoscope::Plugin {
 
   EventHandlerResult beforeReportingState();
   EventHandlerResult onLayerChange();
+  EventHandlerResult onSetup() {
+    return onLayerChange();
+  }
 
  private:
   static bool highlight_normal_modifiers_;