systemc: Handle null and omitted event names.
systemc: Handle null and omitted event names.

If the simulation isn't running, these should be replaced with versions
generated by sc_gen_unique_name().

Change-Id: Idd515e73ba17d3dfa866ee5509369e9c4e3fb2f5
Reviewed-on: https://gem5-review.googlesource.com/12258
Reviewed-by: Gabe Black <5c8aa1266c03186393d9e7b3b4e3b14239af8201@google.com>
Maintainer: Gabe Black <5c8aa1266c03186393d9e7b3b4e3b14239af8201@google.com>

TUD-OS/gem5-dtu,gem5/gem5,TUD-OS/gem5-dtu,TUD-OS/gem5-dtu,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,TUD-OS/gem5-dtu,TUD-OS/gem5-dtu,TUD-OS/gem5-dtu,gem5/gem5,TUD-OS/gem5-dtu