use assert(0) instead of exit(1)

use assert(0) instead of exit(1)

When a fatal error (unaligned memory etc.) is detected, jerasure
should assert(3) instead of exit(3) to give a chance to the calling
program to catch the exception and display a stack trace. Although it is
possible for gdb to display the stack trace and break on exit, libraries
are not usually expected to terminate the calling program in this way.

Signed-off-by: Loic Dachary <loic@dachary.org>