speex resampler: add 10% slack output space

This should fix buffer underflows when changing the playback rate.
We probably should instead reallocate the buffer and resume resampling
when the situation occurs, but that would be a lot more complicated.
(cherry picked from commit 86d9aabfe7e62477b6f6bb15a61c47df159c813f)

modules/audio_filter/resampler/speex.c

@@ -111,7 +111,7 @@ static block_t *Resample (filter_t *filter, block_t *in)
     const unsigned orate = filter->fmt_out.audio.i_rate;
 
     spx_uint32_t ilen = in->i_nb_samples;
-    spx_uint32_t olen = ((ilen + 2) * orate) / irate;
+    spx_uint32_t olen = ((ilen + 2) * orate * 11) / (irate * 10);
 
     block_t *out = block_Alloc (olen * framesize);
     if (unlikely(out == NULL))