[#969] Fixes linux AppImage

StartupWMClass matches what SDL reports: AppRun execs bin/love, so the
window's WM_CLASS / Wayland app_id is "love" and without this the taskbar
entry never resolves back to this desktop file (no name, no icon).

scripts/linux-arm64/build_appimage.sh

@@ -369,6 +369,7 @@ Name=gen1recomp
 Comment=Pokémon Gen 1 recompilation
 Exec=$APP_NAME
 Icon=$APP_NAME
+StartupWMClass=love
 Categories=Game;
 Terminal=false
 EOF