BACKPORT: Uninstalled pike without args accesses free block

Imported from http://bugzilla.roxen.com/bugzilla/show_bug.cgi?id=3523

Reported by Martin Nilsson, IDA nilsson@pike.ida.liu.se

[nilsson@mahoro dmalloc]$ ./pike
Couldn't load master program from NONE/pike/7.5.12/lib/master.pike.
Access to free block: 0x9570540 (size 92)!
Locations that handled 0x9570540: (gc generation: 0/0  gc pass: 0/0)
*** /home/nilsson/Pike/7.5/src/stralloc.c:576 xalloc (1 times) !*!
*** /home/nilsson/Pike/7.5/src/modules/files/efuns.c:599 sub_ref (1 times) !*!
*** /home/nilsson/Pike/7.5/src/pike_memory.c:574 malloc (1 times) !*!
*** /home/nilsson/Pike/7.5/src/stralloc.c:788 add_ref (1 times)
*** /home/nilsson/Pike/7.5/src/error.c:687 (1 times) !*!
*** /home/nilsson/Pike/7.5/src/main.c:736 (1 times) !*!
*** /home/nilsson/Pike/7.5/src/modules/files/efuns.c:599 (1 times) !*!
*** /home/nilsson/Pike/7.5/src/stralloc.c:783 (1 times)
*** /home/nilsson/Pike/7.5/src/stralloc.c:885 (1 times)
*** /home/nilsson/Pike/7.5/src/stralloc.c:970 (1 times) !*!
Aborted