Check for invalid handle before looking up device by handle

When invalid connection handle is passed to btm_find_dev_by_handle(), it returns the first device which does not have any of the transports connected.

Test: mmm packages/modules/Bluetooth
Flag: EXEMPT trivial fix
Bug: 399122843
Change-Id: Idedd4a65ed4517ae6bee7efda9b0f87b7096a8c2