Fix uninitialized LogConfig member variable

[bneradt]

Valgrind reported a conditional jump depending on an uninitialized value in Log::periodic_tasks(). The root cause was that roll_log_files_now was not initialized in LogConfig. While we're at it, I'm initializing m_partition_space_left in the member declaration as well.

Fixed by adding default member initializers in the class definition, consistent with the other members.

Valgrind report that reported this:

  Thread 30 [LOG_FLUSH]:
  Conditional jump or move depends on uninitialised value(s)
     at 0x68F310: Log::periodic_tasks(long)
     by 0x6901FF: Log::flush_thread_main(void*)
     by 0x695FEC: LoggingFlushContinuation::mainEvent(int, void*)
     by 0x883EA2: EThread::execute()
     by 0x87FD61: spawn_thread_internal(void*)
   Uninitialised value was created by a heap allocation
     at 0x4C2A593: operator new(unsigned long)
     by 0x695440: Log::init(int)

[cmcfarlen]

I wonder if coverity found this?

[bneradt]

Thanks for the review.

I wonder if coverity found this?

Maybe coverity could have found it? I found it via the valgrind run I mentioned in the description while trying to track down a different issue.