Fixes leak introduced by e562e82f

==4937== 64 bytes in 1 blocks are definitely lost in loss record 270 of 405
==4937==    at 0x4A06BE0: realloc (vg_replace_malloc.c:662)
==4937==    by 0x6FA41C4: __vasprintf_chk (vasprintf_chk.c:90)
==4937==    by 0x50C8D29: virVasprintfInternal (stdio2.h:199)
==4937==    by 0x50C8E3A: virAsprintfInternal (virstring.c:362)
==4937==    by 0x11D01A: main (libvirtd.c:1170)
Signed-off-by: NJán Tomko <jtomko@redhat.com>