#775 Fix and related test for issue #772

Reece, I couldn't figure out, how to properly test too small buffer from tests/api.c, but I created tests/mbrola.test for MBROLA voice and checked, that if line is set to espeak_Initialize(AUDIO_OUTPUT_SYNCHRONOUS, 1, data_path, 0); in espeak-ng.c, test fails. It may also help in future changes in implementation of eSpeak NG.

[espeak-ng:master] New Comment on Issue #772 Setting buffer size to 50ms leads to truncated mbrola-fr4 output
By valdisvi:

@rhdunn, I created pull request #775 of the fix for your review.