Release DrmManagerClient resources

Call release for DrmManagerClient to avoid resource leaks

Introduced by following commit (5d143ad4a8f...),
"Media scanner support for FL(Forward Lock) DRM file types"

https://android-review.googlesource.com/#/c/91081/

Change-Id: Ic3c458579f4e99b3b072a2e13362d1996b982589
Media process is crashing with NullPointer exception

Sometime, while creating thumnails list of media files in
compose MMS->attach file,  filepath may be null due to
synchronization issue.
Adding NULL check to avoid NUllPointer exception.

Change-Id: Id6cf5612a959b3ae15b44bc60dbbcbe40c624f09
CRs-Fixed: 636494