gdb: restore displaced step buffer bytes when another thread forks

gdb: restore displaced step buffer bytes when another thread forks

In handle_inferior_event, where we handle forks, we make sure to restore
the bytes of the displaced stepping buffer in the child's address
space.  However, we only do it when the forking thread was the one
doing a displaced step.  It could happen that a thread forks while
another one is doing a displaced step.  In this case, we also need to
restore the bytes in the child.

Move the byte-restoring code outside of the condition that checks
whether the event thread was displaced stepping.

gdb/ChangeLog:

	* infrun.c (handle_inferior_event): Restore displaced step
	buffer bytes in child process when handling fork, even if fork
	happened in another thread than the displaced-stepping one.

Change-Id: Ibb0daaeb123aba03f4fb4b4d820754eb2436bc69