fix docker entrypoint failures when gid is defined but not uid (#521)

entrypoint.sh

@@ -9,6 +9,8 @@ ONEDRIVE_GID=$(stat /onedrive/data -c '%g')
 if ! odgroup="$(getent group $ONEDRIVE_GID)"; then
   odgroup='onedrive'
   groupadd "${odgroup}" -g $ONEDRIVE_GID
+else
+  odgroup=${odgroup%%:*}
 fi
 
 # Create new user using target UID
@@ -17,7 +19,6 @@ if ! oduser="$(getent passwd $ONEDRIVE_UID)"; then
   useradd "${oduser}" -u $ONEDRIVE_UID -g $ONEDRIVE_GID
 else
   oduser="${oduser%%:*}"
-  odgroup="${odgroup%%:*}"
   usermod -g "${odgroup}" "${oduser}"
   grep -qv root <( groups "${oduser}" ) || { echo 'ROOT level priviledges prohibited!'; exit 1; }
 fi