Unhandled KeyError Exception

[labishrestha2]

In ble_adapter.py, there are several spots where the dict values are accessed without checking if they exist, that causes KeyErrors.

For e.g. in ble_adapter.py : 272:

 @NordicSemiErrorCheck(expected=BLEGattStatusCode.success)
    def service_discovery(self, conn_handle, uuid=None):
        vendor_services = []
        self.driver.ble_gattc_prim_srvc_disc(conn_handle, uuid, 0x0001)

        while True:
            response = self.evt_sync[conn_handle].wait(  # Here sometimes, the conn_handle could not be in the evt_sync dict
                evt=BLEEvtID.gattc_evt_prim_srvc_disc_rsp
            )

            if response["status"] == BLEGattStatusCode.success: # Here the response can be None, or it may not contain "status"
                for s in response["services"]:
                    if s.uuid.value == BLEUUID.Standard.unknown:

I've found that every now and then the BLE service discovery will fail because of a KeyError here or sometimes a None response is returned. Adding a Key check and None check here seems to fix most of the disconnections during discovery.

I'll go ahead and submit PR with my changes. Feel free to iterate.

Thank you