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
Merge "Media process is crashing with NullPointer exception" into kitkat