RPCMuon bugfix in MuonIdProducer

The RPCMuon is mis-implemented as a subset of TrackerMuons.
Originally it is designed to be a complementary ones to the TM's.
I think this code should stay unchanged to preserve the old behavior
```
if(!muon.isTrackerMuon() && isAlsoTkMu_) return false;
```
otherwise, with the change in the code, the results change.
Note that the code below the ifs will be reached only if the muon isGlobal, which always have a track and would never crash. (It's not obvious that with a flag isAlsoTkMu the global.notTracker.rpc muons are a trivially good addition)