Makes it safe if somehow the WAYLAND_DISPLAY env var is set but incorrectly.

Inspired by qurious' solution.

scripts/generate_appimages.sh

@@ -95,7 +95,7 @@ cp /usr/lib/x86_64-linux-gnu/dri/swrast_dri.so ${BUILD_DIR}/duckstation-qt.AppDi
 cp -r /usr/lib/x86_64-linux-gnu/qt5/plugins/{xcbglintegrations,platforms,wayland-graphics-integration-client,wayland-decoration-client,wayland-shell-integration} ${BUILD_DIR}/duckstation-qt.AppDir/usr/plugins
 
 cat <<'EOF'>> ${BUILD_DIR}/duckstation-qt.AppDir/apprun-hooks/linuxdeploy-plugin-qt-hook.sh
-if [ ! -z "${WAYLAND_DISPLAY}" ]; then
+if [[ "${WAYLAND_DISPLAY}" == "wayland"* ]]; then
 	if [ -z ${QT_QPA_PLATFORM} ]; then
 		export QT_QPA_PLATFORM=wayland
 	fi