C2SoftAac: fix error handling

- Handle zero-length data.
- Do not return prematurely for corrupted data.

Bug: 74073134
Test: adb shell setprop debug.stagefright.ccodec yes
Test: adb shell setprop debug.stagefright.omx_default_rank 1000
Test: adb shell killall mediaserver
Test: atest android.media.cts.MediaCodecTest
Change-Id: I641c3200b9817d44e3e938c03a5d796857ed1be7
(cherry picked from commit b210d635)