erp5: resiliency-after-import script of mariadb shouldn't fail if there is no binlog

If there is no binlog in srv/backup/mariadb-incremental (ie : the parameter
incremental_backup_retention_days is set to -1), then the import script fails.
This should not happen as this script just updates some inline paths.
This commit just add a correct check on variables and files existence

stack/erp5/buildout.cfg

@@ -150,7 +150,7 @@ command = grep parts ${buildout:develop-eggs-directory}/slapos.cookbook.egg-link
 [mariadb-resiliency-after-import-script]
 recipe = slapos.recipe.build:download
 url = ${:_profile_base_location_}/template/instance-mariadb-resiliency-after-import-script.sh.in
-md5sum = b32d9ee1cb85f85d8d2f2b58f58459f1
+md5sum = 79109ae720d5471cb2dd15e63fdf4dcf
 mode = 755
 
 [template-mariadb]

stack/erp5/template/instance-mariadb-resiliency-after-import-script.sh.in

@@ -32,11 +32,16 @@ fi
 echo "Deleting existing database..."
 rm -r $mariadb_data_directory/* >/dev/null 2>&1 || true
 
-echo "Adapting binlog database to new paths..."
-new_binlog_directory="$(dirname $binlog_path)"
-binlog_index_file="$new_binlog_directory/binlog.index"
-old_binlog_directory="$(dirname $(head -n 1 $binlog_index_file))"
-sed -e "s|$old_binlog_directory|$new_binlog_directory|g" $binlog_index_file > $binlog_index_file
+# $binlog_path can be empty if incremental_backup_retention_days <= -1
+if [ -n "$binlog_path" ]; then
+  new_binlog_directory="$(dirname $binlog_path)"
+  binlog_index_file="$new_binlog_directory/binlog.index"
+  if [ -e "$binlog_index_file" ]; then
+    echo "Adapting binlog database to new paths..."
+    old_binlog_directory="$(dirname $(head -n 1 $binlog_index_file))"
+    sed -e "s|$old_binlog_directory|$new_binlog_directory|g" $binlog_index_file > $binlog_index_file
+  fi
+fi
 
 echo "Starting mariadb..."
 # XXX hardcoded