#118 Fix CVE-2019-13590

[Judy Hsiao]

bug reference: https://sourceforge.net/p/sox/bugs/325/
This issue is also reported as CVE-2019-13590

Patch Detail:
Fix sox-14.4.2 NULL pointer dereference on lsx_readbuf in formats_i.c by
doing a prior check that it is a valid pointer before passing into lsx_calloc.

Test: run soxi sox-fmt_56_integer_overflow.mp3.
The soxi command should return a error: "premature EOF" rather than giving
a core dump.

[Mans Rullgard]

This doesn't fix the bug.