dyn PDCH: safeguard: exit if nothing pending in dyn_pdch_ts_disconnected()
dyn PDCH: safeguard: exit if nothing pending in dyn_pdch_ts_disconnected()

The function would currently only be called in cases where one of the if
branches catches on, but for safety's and clarity's sake, don't ts_connect
using as_pchan if no reconnect is pending.

Change-Id: I52c34065254e902bb80662fc04540901b36cb4c3

osmocom/osmo-bts,osmocom/osmo-bts,osmocom/osmo-bts