voamrwbenc: Fix truncation of audio data at end-of-stream when audio data doesn't align on 20 millisecond frame size.

voamrwbenc: Fix truncation of audio data at end-of-stream when audio data doesn't align on 20 millisecond frame size.

The AMR-WB codec imposes a fixed 20 millisecond frame size. In its current form, the voamrwbenc plugin deals with this limitation by discarding any audio at the end of the stream that falls short of 20 milliseconds. This patch keeps the audio data, and appends silence to the end to preserve frame size alignment.

The patch also adds tests to check for the updated behavior. I noticed that tests weren't being built, so I changed the build to allow for building the tests when the tests and voamrwbenc options are set.