libstagefright: Fix for video can't be played if BT is connected

-Issue: Video can't be played if BT is connected.
-Rootcause: Source code to handle fallback to software decoder
 if offload audio track creation fails is not present.
-Fix: Add source code to handle fallback to software decoder
 if offload audio track creation fails.

Change-Id: Ie136a2117dd3f028c962b8b73ebc238bc982d79b
CRs-Fixed:  593230