crash when snapshot isn't enabled, but try to use it anyway

```
[ERROR] SNAPSHOT ISOLATION REQUIRES MODIFICATIONS TO THE LRL FILE
[ERROR] unable to set_transaction_mode
[ERROR] put_curtran_int called without curtran
Comdb2's Linux Cheap Stack Trace :: pthread_self:140736838940416 @ ../db/sqlglue.c:8811
tid=0x7fffd94ab700(3645552384) stack trace, run addr2line -f -e on:
0x592b39 0x592ccc 0x5ab05d 0x5ab12f 0x70e87d 0x7ffff65ac6ba 0x7ffff62e241d (nil)
[ERROR] sqlengine_work_appsock: unable to destroy a CURSOR transaction!
[FATAL] couldnt get clnt->write_lock
[Inferior 1 (process 11177) exited with code 01]
(gdb)
```