Fix corrupted HEALTH_URL and ASCII art in Dockerfiles caused by version updater

The addons_updater script's global sed replacement corrupted Dockerfiles
when the upstream_version was empty (""), replacing all empty double-quoted
strings with version strings. This corrupted:

- HEALTH_URL values (causing malformed health check URLs and container
  instability from failed health checks)
- ASCII art comments in Dockerfile headers

Fixed affected addons: guacamole, tdarr, photoprism, enedisgateway2mqtt_dev,
gazpar2mqtt, seafile

Also added a guard in the updater script to skip updates when version
strings are empty, preventing this corruption from recurring.

Co-authored-by: alexbelgium <44178713+alexbelgium@users.noreply.github.com>

addons_updater/rootfs/etc/cont-init.d/99-run.sh

@@ -319,6 +319,12 @@ for f in */; do
         LASTVERSION2=${LASTVERSION//+/-}
         CURRENT2=${CURRENT//+/-}
 
+        # Skip if current or last version is empty (would corrupt files by replacing all "" occurrences)
+        if [ "${CURRENT}" = '""' ] || [ "${LASTVERSION}" = '""' ]; then
+            bashio::log.warning "... $SLUG : skipping update due to empty version string (current=${CURRENT}, latest=${LASTVERSION})"
+            continue
+        fi
+
         # Update if needed
         if [ "${CURRENT2}" != "${LASTVERSION2}" ]; then
             LOGINFO="... $SLUG : update from ${CURRENT} to ${LASTVERSION}" && if [ "$VERBOSE" = true ]; then bashio::log.info "$LOGINFO"; fi