OemHook missing but called: don't infinite loop

The previous code assumes that if an IOemHook related method
is called that IOemHook is on the device.

The infinite loop:
-> getOemHookProxy
-> getService return null
-> EVENT_RADIO_PROXY_DEAD sent
-> getOemHookProxy(null) called

Bug: 78299964
Test: cuttlefish 4G working
Change-Id: Ia841c6fdee6706a7e2fc857a378dab154d07acff