No interactions found -> crash of RawRecordsFromMcChain

[PavelKavrigin]

Currently, when we use RawRecordsFromMcChain plugin, if there are no interactions found by epix, it will cause a crash with this error:

        Traceback (most recent call last):
          File "run_wfsim.py", line 120, in <module>
            st.make(args.run_id, 'raw_records')
          File "/opt/XENONnT/anaconda/envs/XENONnT_development/lib/python3.8/site-packages/strax/context.py", line 1411, in make
            for _ in self.get_iter(run_ids[0], targets,
          File "/opt/XENONnT/anaconda/envs/XENONnT_development/lib/python3.8/site-packages/strax/context.py", line 1263, in get_iter
            components = self.get_components(run_id,
          File "/opt/XENONnT/anaconda/envs/XENONnT_development/lib/python3.8/site-packages/strax/context.py", line 1024, in get_components
            d.setup()
          File "/opt/XENONnT/anaconda/envs/XENONnT_development/lib/python3.8/site-packages/wfsim/strax_interface.py", line 556, in setup
            self.get_instructions()
          File "/opt/XENONnT/anaconda/envs/XENONnT_development/lib/python3.8/site-packages/wfsim/strax_interface.py", line 809, in get_instructions
            self.set_timing()
          File "/opt/XENONnT/anaconda/envs/XENONnT_development/lib/python3.8/site-packages/wfsim/strax_interface.py", line 819, in set_timing
            % (self.config['entry_stop'], np.min(self.g4id), np.max(self.g4id)))
          File "<__array_function__ internals>", line 180, in amin
          File "/opt/XENONnT/anaconda/envs/XENONnT_development/lib/python3.8/site-packages/numpy/core/fromnumeric.py", line 2916, in amin
            return _wrapreduction(a, np.minimum, 'min', axis, None, out,
          File "/opt/XENONnT/anaconda/envs/XENONnT_development/lib/python3.8/site-packages/numpy/core/fromnumeric.py", line 86, in _wrapreduction
            return ufunc.reduce(obj, axis, dtype, out, **passkwargs)
        ValueError: zero-size array to reduction operation minimum which has no identity

This exception must be handled, and it would also make sense to check beforehand if there're any interactions to process or not. As for now, WFSim crashes, and it triggers useless job resubmissions if we use mc_chain.