Stupid error, easy to reproduce, simple fix.

+++ This bug was initially created as a clone of Bug #785290 +++

Description of problem:

$ ocaml 
        Objective Caml version 3.12.1

# #use "topfind";;
- : unit = ()
Findlib has been successfully loaded. Additional directives:
  #require "package";;      to load a package
  #list;;                   to list the available packages
  #camlp4o;;                to load camlp4 (standard syntax)
  #camlp4r;;                to load camlp4 (revised syntax)
  #predicates "p,q,...";;   to set these predicates
  Topfind.reset();;         to force that packages will be reloaded
  #thread;;                 to enable threads

- : unit = ()
# #require "guestfs";;
/usr/lib64/ocaml/unix.cma: loaded
/usr/lib64/ocaml/guestfs: added to search path
/usr/lib64/ocaml/guestfs/mlguestfs.cma: loaded
# #use "/usr/share/doc/ocaml-libguestfs-devel-1.17.2/create_disk.ml";;
val output : string = "disk.img"
libguestfs: trace: set_autosync true
libguestfs: trace: set_autosync = 0
Segmentation fault

Version-Release number of selected component (if applicable):

1.17.2

How reproducible:

100% (bytecode)
Doesn't segfault in native code.

--- Additional comment from rjones on 2012-01-27 16:42:00 EST ---

Stack trace:

#0  __strlen_sse2 () at ../sysdeps/x86_64/strlen.S:32
#1  0x0000003a24686a76 in __GI___strdup (s=0x1 <Address 0x1 out of bounds>)
    at strdup.c:42
#2  0x00007ffff109bd8c in guestfs_safe_strdup ()
   from /usr/lib64/libguestfs.so.0
#3  0x00007ffff1335f76 in ocaml_guestfs_add_drive_opts (gv=1, readonlyv=1, 
    formatv=140737352560936, ifacev=1, namev=1, filenamev=1)
    at guestfs_c_actions.c:732
#4  0x000000000041b3d1 in caml_interprete (prog=0x7ffff7bd2010, 
    prog_size=<optimized out>) at interp.c:905
#5  0x000000000041cf73 in caml_main (argv=0x7fffffffdf08) at startup.c:424
#6  0x0000000000409dbc in main (argc=<optimized out>, argv=<optimized out>)

Note in frame #3 that filenamev is bogus; it should be
a string value.

--- Additional comment from rjones on 2012-01-27 17:36:04 EST ---

Fixed:
https://github.com/libguestfs/libguestfs/commit/799852e64691068f3256c27d18870bdb2537c2be
https://github.com/libguestfs/libguestfs/commit/eb68a314133c88260cdf4547d7d338446488e698