Investigate index out of bounds exception when no bios are logged

[ashmrtn]

The test harness portion of CrashMonkey crashes with an index out of bounds exception when no bios are logged/transferred to user space.

Running sudo ./c_harness -f /dev/vda -d /dev/cow_ram0 -t btrfs -e 102400 tests/rename_root_to_sub.so on a build from master should trigger this bug (potentially substituting /dev/vda with an existing disk in the VM).

[ashmrtn]

Bug is most likely caused by a negative index into the vector of operations in the gen_one_state method of RandomPermuter. RandomPermuter or Permuter should be modified to return immediately with a return value of false if there are no operations to permute.