Fixed a bug with extra being nullptr when _host_view is true: always allocate extra

(Note that BaseAmoeba has its own cast_extra_data() that doesn't know if extra is allocated properly, it is the case when _host_view is false for dedicated GPUs for example)

lib/gpu/lal_atom.cpp

@@ -124,7 +124,7 @@ bool AtomT::alloc(const int nall) {
                                    UCL_READ_ONLY)==UCL_SUCCESS);
     gpu_bytes+=v.device.row_bytes();
   }
-  if (_extra_fields>0 && !_host_view) {
+  if (_extra_fields>0) {
     success=success && (extra.alloc(_max_atoms*_extra_fields,*dev,UCL_WRITE_ONLY,
                                    UCL_READ_ONLY)==UCL_SUCCESS);
     gpu_bytes+=extra.device.row_bytes();