winbindd can crash with segv in dcerpc_binding_handle_call_send()

Issue

• winbindd can crash with segv in dcerpc_binding_handle_call_send()

Sample call trace:

$ grep systemd-coredump /var/log/messages | grep winbindd | sed -e 's/#012/\n#012/g'
<DATE> <HOSTNAME> systemd-coredump[XXXX]: Process YYYY (winbindd) of user 0 dumped core.
#012
#012Stack trace of thread ZZZZ:
#012#0  0x00007f7e48f2b37f raise (libc.so.6)
#012#1  0x00007f7e48f15db5 abort (libc.so.6)
#012#2  0x00007f7e4ad9e4a4 dump_core (libsmbconf.so.0)
#012#3  0x00007f7e4adad420 smb_panic_s3 (libsmbconf.so.0)
#012#4  0x00007f7e4b09a5de smb_panic (libsamba-util.so.0)
#012#5  0x00007f7e4b09a669 sig_fault (libsamba-util.so.0)
#012#6  0x00007f7e4a1e8c20 __restore_rt (libpthread.so.0)
#012#7  0x00007f7e4b6ebb76 dcerpc_binding_handle_call_send (/usr/lib64/libdcerpc-binding.so.0.0.1)
#012#8  0x00007f7e4b5d2a05 dcerpc_wbint_GetNssInfo_r_send (/usr/lib64/samba/libdcerpc-samba4.so)
#012#9  0x00007f7e4b5d2d76 dcerpc_wbint_GetNssInfo_send (/usr/lib64/samba/libdcerpc-samba4.so)
#012#10 0x000055986f635877 wb_queryuser_got_domain (winbindd)
#012#11 0x000055986f631922 wb_lookupsid_done (winbindd)
#012#12 0x00007f7e4b6eb821 dcerpc_binding_handle_call_done (/usr/lib64/libdcerpc-binding.so.0.0.1)
#012#13 0x000055986f625951 wbint_bh_raw_call_domain_done (winbindd)
#012#14 0x000055986f623260 wb_domain_request_done (winbindd)
#012#15 0x000055986f621281 wb_child_request_done (winbindd)
#012#16 0x000055986f646bbb wb_simple_trans_read_done (winbindd)
#012#17 0x000055986f6463ea wb_resp_read_done (winbindd)
#012#18 0x00007f7e49ad8d87 tevent_common_invoke_fd_handler (libtevent.so.0)
#012#19 0x00007f7e49adf50f epoll_event_loop_once (libtevent.so.0)
#012#20 0x00007f7e49add4fb std_event_loop_once (libtevent.so.0)
#012#21 0x00007f7e49ad81e5 _tevent_loop_once (libtevent.so.0)
#012#22 0x000055986f5ca4fc main (winbindd)
#012#23 0x00007f7e48f17493 __libc_start_main (libc.so.6)
#012#24 0x000055986f5caefe _start (winbindd)