These represent the mouse entering a client window child, and if no
MotionNotify events follow, we'll be left out of sync with X.

Signed-off-by: Alexandre Julliard <julliard@winehq.org>

Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=53783

This moves unsafe_block_from_ptr calls outside of the heap lock.

We assume here that concurrent call to another heap function on a block
being freed is undefined, and it should then be safe to do so:

* The block type or base offset never change after a block has been
  allocated and until it is freed.

* Block flags such as BLOCK_FLAG_LARGE, or BLOCK_FLAG_USER_INFO also
  never change after a block has been allocated.

* Other block flags are only read and modified inside the heap lock.