util: Avoid Coverity FORWARD_NULL

util: Avoid Coverity FORWARD_NULL

Avoid a false positive since Coverity find a path in virResizeN which
could return 0 prior to the allocation of memory and thus flags a
possible NULL dereference. Instead allocate the output buffer based
on 'nparams' and only fill it partially if need be - shouldn't be too
much a waste of space. Quicker than multiple VIR_RESIZE_N calls or
two loops of STREQ's sandwiched around a single VIR_ALLOC_N using
'n' matches from a first loop to generate the 'n' addresses to return

Signed-off-by: John Ferlan <jferlan@redhat.com>