picoTTS text input buffer is 4 + 256 = 260 bytes

for en_GB picoTTS needs ~2MB of memory

There is a bug in picosig2.c:555 which causes 4 bytes overflow in memset which in turn
makes size filed bogus in other struct which gives segfault when releasing the resources.
Thanks to http://dept-info.labri.fr/~thibault/gdb.html.en