be more diligent with bounding box information when reading from a data file or checking it

src/read_data.cpp

@@ -347,6 +347,8 @@ void ReadData::command(int narg, char **arg)
   nbonds = nangles = ndihedrals = nimpropers = 0;
   nbondtypes = nangletypes = ndihedraltypes = nimpropertypes = 0;
   triclinic = 0;
+  boxlo[0] = boxlo[1] = boxlo[2] = 0.0;
+  boxhi[0] = boxhi[1] = boxhi[2] = 0.0;
   keyword[0] = '\0';
 
   nlocal_previous = atom->nlocal;