(master) synaptics: fix missing NULL check + open_slots double-free in DeviceInit()

[metux]

DeviceInit() checked priv->hwState and priv->local_hw_state for
allocation failure but not the third SynapticsHwStateAlloc() call
(priv->comm.hwState) -- SynapticsReset(), called right after, derefs
it unconditionally.

Separately, the 'fail' cleanup path used raw free() on hwState/
local_hw_state instead of SynapticsHwStateFree() (leaking their
nested slot_state/mt_mask allocations), and freed priv->open_slots
without resetting it to NULL. priv survives a failed DeviceInit() and
SynapticsUnInit() later frees priv->open_slots again if it's
still non-NULL, so this was a double-free on the open_slots
allocation failure or the hwState allocation failure path.

Add the missing check, use SynapticsHwStateFree() for symmetry with
DeviceClose()'s normal-path cleanup, and NULL out open_slots after
freeing it.

Signed-off-by: Enrico Weigelt, metux IT consult info@metux.net

[metux]

Note: could not locally build-verify this change — autogen.sh/configure.ac here requires
xorg-server >= 25.0.0 via pkg-config, and this host's registered system package is 21.1.16.
The change itself is a minimal, mechanical NULL-check following the exact pattern already used a
few lines above the touched code in the same function — flagging the verification gap rather than
silently claiming it was tested.