luci-app-mosdns: Clean cache.dump file when "Save Cache" is disabled

luci-app-mosdns/root/etc/init.d/mosdns

@@ -64,7 +64,8 @@ init_yaml() {
 	s,maximum_ttl_custom,$maximum_ttl_custom,g; \
 	s,adblock,$adlist,g;s,remote_dns_pipeline,$enable_pipeline,g" \
 	/usr/share/mosdns/default.yaml > $CONF
-	[ "$dump_file" -eq 1 ] && sed -i "/lazy_cache_ttl/a\      dump_file: /etc/mosdns/cache.dump\n      dump_interval: $dump_interval" $CONF
+	[ "$dump_file" -eq 1 ] && sed -i "/lazy_cache_ttl/a\      dump_file: /etc/mosdns/cache.dump\n      dump_interval: $dump_interval" $CONF || \
+	\cp -a /usr/share/mosdns/cache.dump /etc/mosdns/cache.dump
 	echo "${local_dns}" > $tmpdir/local_dns.txt
 	echo "${remote_dns}" > $tmpdir/remote_dns.txt
 	sed -i -e '/- addr: local_dns/{r '$tmpdir/local_dns.txt -e';d};/- addr: remote_dns/{r '$tmpdir/remote_dns.txt -e';d}' \