fix(sim): Clarify behaviour for same-name sensitive volumes

The transport engines allow registering of multiple nodes
with the same volume/same volume name (copy mechanism).
In `FairRoot` this mechanism works provided unique volume name
over the whole geometry setup of different detectors.

The commit clarifies the situtation:
1. for same volume names in one detector, it quenches the log message
by moving `LOG` and changing it severity
from `LOG(error)` in `FairVolumeList::addVolume()`
to `LOG(debug)` in `FairModule::AddSensitiveVolume()`.
2. for same volume names accross different detectors,
it crashes the program with appropriate `LOG(fatal)`.

Fixes the issue #1595.

fairroot/base/sim/FairModule.cxx

@@ -280,8 +280,9 @@ void FairModule::AddSensitiveVolume(TGeoVolume* vol)
     auto volName = vol->GetName();
     LOG(debug2) << "AddSensitiveVolume " << volName;
 
-    auto addedVol = vList->addVolume(std::make_unique<FairVolume>(volName, fNbOfVolumes));
+    auto addedVol = vList->addVolume(std::make_unique<FairVolume>(volName, fNbOfVolumes, 0, this));
     if (!addedVol) {
+        LOG(debug) << "FairModule: Trying to register element " << vol->GetName() << " for detector " << GetName() << " failed, beacuse it was already defined";
         return;
     }
     ++fNbOfVolumes;

fairroot/base/sim/FairVolumeList.cxx

@@ -11,6 +11,8 @@
 // -------------------------------------------------------------------------
 
 #include "FairVolumeList.h"
+#include "FairVolume.h"
+#include "FairDetector.h"
 
 FairVolume* FairVolumeList::getVolume(const TString& name)
 {
@@ -34,13 +36,20 @@ FairVolume* FairVolumeList::addVolume(std::unique_ptr<FairVolume> vol)
 {
     auto vol_found = findObject(vol->GetName());
 
+    auto vol_added = static_cast<FairVolume*>(vol.get());
+
+    // FATAL: The same volume name for different detectors
+    if (vol_found && vol->GetDetector() != vol_found->GetDetector() ) {
+        LOG(fatal) << "FairVolumeList Trying to register element: " << vol->GetName() << " (VolId=" << vol->getVolumeId()
+                   << ") for detector " << vol->GetDetector()->GetName() << ", but it was already defined (VolId="
+                   << vol_found->getVolumeId() << ") for detector " << vol_found->GetDetector()->GetName();
+        std::terminate();
+        return nullptr;
+    }        
     if (vol_found) {
-        LOG(error) << "FairVolumeList element: " << vol->GetName() << " VolId : " << vol->getVolumeId()
-                   << " already defined " << vol_found->getVolumeId();
         return nullptr;
     }
 
-    auto vol_added = vol.get();
     fData.Add(vol.release());
     return vol_added;
 }