Fix: poll max size should be checked during resize

This was detected using cppcheck:

[src/common/compat/compat-poll.c:204]: (error) Uninitialized variable:
new_size

So, the check was always made over an uninitialized variable on the
stack. Fortunately, worst case scenario, new_size is set to the maximum
allowed or kept untouched.

Signed-off-by: David Goulet <dgoulet@efficios.com>