[MUON] fix data sources when only MFT and MCH are available (#2263)

The case where only MFT and MCH tracks are available was not correctly handled
by the TracksTask, since the standalone MFT and MCH tracks were not
added to the list of requested data sources for the reco container.

This led to fatal exceptions like this during the processing:
```
stderr: what(): [MuonTrack(GlobalFwdTrack)] bad MFT track index: iMFT=1417 tracksMFT.size()=0
```

Modules/MUON/Common/src/TracksTask.cxx

@@ -48,6 +48,11 @@ GID::mask_t adaptSource(GID::mask_t src)
     src.set(GID::Source::MCH);
     src.set(GID::Source::MID);
   }
+  if (src[GID::Source::MFTMCH] == 1) {
+    // ensure we request the individual tracks as we use their information in the plotter
+    src.set(GID::Source::MFT);
+    src.set(GID::Source::MCH);
+  }
   if (src[GID::Source::MCHMID] == 1) {
     // ensure we request the individual tracks as we use their information in the plotter
     src.set(GID::Source::MCH);
@@ -261,9 +266,6 @@ void TracksTask::monitorData(o2::framework::ProcessingContext& ctx)
     return;
   }
 
-  auto tracksMCH = ctx.inputs().get<gsl::span<o2::mch::TrackMCH>>("trackMCH");
-  auto clusters = ctx.inputs().get<gsl::span<o2::mch::Cluster>>("trackMCHTRACKCLUSTERS");
-
   ILOG(Debug, Devel) << "Debug: Asserted inputs" << ENDM;
 
   mRecoCont.collectData(ctx, *mDataRequest.get());