lib/lib-logging.c: fix GCC warning: check return value of snprintf()

lib/lib-logging.c: fix GCC warning: check return value of snprintf()

This patch fixes this GCC warning:

    lib-logging.c: In function ‘format_component’:
    lib-logging.c:110:44: error: ‘%s’ directive output may be truncated
    writing 10 bytes into a region of size between 0 and 127
    [-Werror=format-truncation=]
       snprintf(tmp_prefix, TMP_PREFIX_LEN - 1, "%s%s", \
                                                ^~~~~~
         prefix, (_prefix2));   \
                 ~~~~~~~~~~
    lib-logging.c:1013:3: note: in expansion of macro ‘SET_TMP_PREFIX’
       SET_TMP_PREFIX("so-handle-");
       ^~~~~~~~~~~~~~
    lib-logging.c:110:3: note: ‘snprintf’ output between 11 and 138
    bytes into a destination of size 127
       snprintf(tmp_prefix, TMP_PREFIX_LEN - 1, "%s%s", \
       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
         prefix, (_prefix2));   \
         ~~~~~~~~~~~~~~~~~~~
    lib-logging.c:1013:3: note: in expansion of macro ‘SET_TMP_PREFIX’
       SET_TMP_PREFIX("so-handle-");
       ^~~~~~~~~~~~~~

The macro aborts when the return value is unexpected, but this will
never happen as we control the prefixes internally.

Boosting the buffer's size to 128 just in case.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Change-Id: I6cbb43de3c9ae03b5d85074d1698069084659c3b
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1658