Gl.glGetString dumps core

Imported from http://bugzilla.roxen.com/bugzilla/show_bug.cgi?id=3452

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

Pike v7.4 release 13 running Hilfe v3.5 (Incremental Pike Frontend)
> GL.glGetString(GL.GL_VERSION);

Program received signal SIGSEGV, Segmentation fault.
0x40177833 in strlen () from /lib/libc.so.6
(gdb) bt
#0  0x40177833 in strlen () from /lib/libc.so.6
#1  0x080eed84 in debug_make_shared_string (str=0x0)
    at /home/nilsson/Pike/7.4/src/stralloc.c:872
#2  0x405c228c in f_glGetString ()
   from /usr/local/pike/7.4.13/lib/modules/GL.so
#3  0x0806f096 in opcode_F_CALL_BUILTIN1 (arg1=0)
    at /home/nilsson/Pike/7.4/src/interpret_functions.h:2075
#4  0x0831ce0f in ?? ()
#5  0x080718b6 in o_catch (pc=0x83daa6e "¡\020K!\b\203@\034\022¡")
    at /home/nilsson/Pike/7.4/src/interpret.c:1576
#6  0x0806bdc9 in opcode_F_CATCH ()
    at /home/nilsson/Pike/7.4/src/interpret_functions.h:1201
#7  0x083daa6a in ?? ()
#8  0x080717c0 in mega_apply (type=APPLY_STACK, args=0, arg1=0x0, arg2=0x0)
    at /home/nilsson/Pike/7.4/src/interpret.c:1532
#9  0x080c80d7 in call_pike_initializers (o=0x82a3ae8, args=0)
    at /home/nilsson/Pike/7.4/src/object.c:281
#10 0x080c8304 in parent_clone_object (p=0x82a3ae8, parent=0x0,
    parent_identifier=0, args=0) at /home/nilsson/Pike/7.4/src/object.c:346
#11 0x08070648 in low_mega_apply (type=APPLY_LOW, args=0, arg1=0x8319594,
    arg2=0x18) at /home/nilsson/Pike/7.4/src/apply_low.h:207
#12 0x0806ebb3 in opcode_F_CALL_OTHER_AND_POP (arg1=122)
    at /home/nilsson/Pike/7.4/src/interpret_functions.h:1948
#13 0x082cd546 in ?? ()
#14 0x080717c0 in mega_apply (type=APPLY_STACK, args=0, arg1=0x0, arg2=0x0)
    at /home/nilsson/Pike/7.4/src/interpret.c:1532
#15 0x080723e9 in apply (o=0x82a3bc4, fun=0x0, args=1078309352)
    at /home/nilsson/Pike/7.4/src/interpret.c:1829
#16 0x080c0f35 in main (argc=1, argv=0xbffff354)
    at /home/nilsson/Pike/7.4/src/main.c:726
#17 0x40111907 in __libc_start_main () from /lib/libc.so.6