Fix HDF5 not understanding some files (#313)

* Fix bug in HDF5 that would cause an error during training when the
dataset provides energies with shape (Nsamples,) instead of (Nsamples, 1)

* Accommodate for previous behavior

torchmdnet/datasets/hdf.py

@@ -89,7 +89,10 @@ def _preload_data(self):
                         # Watchout for the 1D case, embed can be shared for all samples
                         tmp = torch.tensor(np.array(data), dtype=dtype)
                         if tmp.ndim == 1:
-                            tmp = tmp.unsqueeze(0).expand(size, -1)
+                            if len(tmp) == size:
+                                tmp = tmp.unsqueeze(-1)
+                            else:
+                                tmp = tmp.unsqueeze(0).expand(size, -1)
                         self.stored_data[field].append(tmp)
                     self.index.extend(list(zip([i] * size, range(size))))
                     i += 1