prlimit: avoid segfault due to array-out-of-bounds error

prlimit: avoid segfault due to array-out-of-bounds error

Example:
$ prlimit -l -l -l -l -l -l -l -l -l -l -l -l -l -l -l -l -l -l -l
RESOURCE DESCRIPTION                         SOFT   HARD UNITS
MEMLOCK  max locked-in-memory address space 65536 262144 bytes
MEMLOCK  max locked-in-memory address space 65536 262144 bytes
...
Segmentation fault

Reported-by: Bernhard Voelker <mail@bernhard-voelker.de>
Signed-off-by: Karel Zak <kzak@redhat.com>