When using a reverse execution command without execution history, GDB
might end up in a state where replaying has been started but remains
at the current instruction. This state is illegal.
Do not step if there is no execution history to avoid this.
2014-05-20 Markus Metzger <markus.t.metzger@intel.com>
* record-btrace.c (record_btrace_step_thread): Check for empty history.