libnbaio: Don't call get_presentation_position for pre KitKat blobs

This fixes a crash with the HTC Tegra3 audio blob where
mStream->get_presentation_position is not NULL but pointing to a unknown
position in memory.

Change-Id: I74855a4c3123a520379a54310d8674e381357e8b
stagefright: Add legacy MediaBuffer::acquireBuffer symbol

Needed by endeavoru libwvm.so.

Change-Id: I8c324f6b0f99d0ea360e875739a2bd564a815cbe