Fix: only pass --conf to flower when flowerconfig.py exists (#14182)

* Fix: only pass --conf to flower when flowerconfig.py exists

The service passes --conf=${PAPERLESS_SRC_DIR}/paperless/flowerconfig.py
unconditionally, but the image does not ship that file. flower 2.0.1 tolerated
this because it ignored a missing config whose basename matched its own default
name; 2.1.0 dropped that basename() call (mher/flower#1391) and now raises
FileNotFoundError, so flower crash-loops and never binds 5555.

Pass the flag only when the file is present.

docker/rootfs/etc/s6-overlay/s6-rc.d/svc-flower/run

@@ -2,6 +2,7 @@
 # shellcheck shell=bash
 
 declare -r log_prefix="[svc-flower]"
+declare -r flower_config="${PAPERLESS_SRC_DIR}/paperless/flowerconfig.py"
 
 echo "${log_prefix} Checking if we should start flower..."
 
@@ -9,12 +10,20 @@ if [[ -n "${PAPERLESS_ENABLE_FLOWER}" ]]; then
 	# Small delay to allow celery to be up first
 	echo "${log_prefix} Starting flower in 5s"
 	sleep 5
-	cd ${PAPERLESS_SRC_DIR}
+	cd "${PAPERLESS_SRC_DIR}" || exit 1
+
+	# Only pass --conf if the file is actually there. The image does not ship one, and
+	# flower >= 2.1.0 exits with FileNotFoundError when an explicitly given --conf path
+	# does not exist (mher/flower#1391). Earlier versions silently ignored it.
+	declare -a conf_args=()
+	if [[ -f "${flower_config}" ]]; then
+		conf_args=(--conf="${flower_config}")
+	fi
 
 	if [[ -n "${USER_IS_NON_ROOT}" ]]; then
-		exec /usr/local/bin/celery --app paperless flower --conf=${PAPERLESS_SRC_DIR}/paperless/flowerconfig.py
+		exec /usr/local/bin/celery --app paperless flower "${conf_args[@]}"
 	else
-		exec s6-setuidgid paperless /usr/local/bin/celery --app paperless flower --conf=${PAPERLESS_SRC_DIR}/paperless/flowerconfig.py
+		exec s6-setuidgid paperless /usr/local/bin/celery --app paperless flower "${conf_args[@]}"
 	fi
 
 else