Since 92e4f02 moved logging logic into store_slow_path function it has
been logging stores even if actually_store parameter is false. Because
of that logging is broken for all atomic instructions. Function "amo" calls
store_slow_path with nullptr argument and actually_store equal to false
while callee uses reg_from_bytes independently from actually_store value
All of that causes dereferencing of nullptr. This commit logs memory
access only if it actually happened
Alexander Romanov