Bluetooth: OPP: null check for optional header length

Adding null check for optional header length in put request
to avoid NUll pointer Exception.

Change-Id: Iac3b96b3803fb0ac83a41e75b7dcc6ce1f7c982f
(cherry picked from commit e880e28f12cdaa53756c69ba6a6ce8e5989602e9)
(cherry picked from commit a18da9aa3e7478934e81e9c73acec3d21842c7dc)
(cherry picked from commit f9d38129e9b1b755f1b3f227521f6054635fe1db)