Only request a palette slice, if we haven't already

This should - in theory - allow other plugins to just use `LEDPaletteTheme`,
without having many copies of the palette.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>

src/Kaleidoscope/LED-Palette-Theme.cpp

@@ -33,7 +33,8 @@ void
 LEDPaletteTheme::begin (void) {
     USE_PLUGINS (&::EEPROMSettings);
 
-    paletteBase = ::EEPROMSettings.requestSlice (16 * sizeof (cRGB));
+    if (!paletteBase)
+      paletteBase = ::EEPROMSettings.requestSlice (16 * sizeof (cRGB));
 }
 
 uint16_t