Prevent segfault if Python was never initialized

src/PYTHON/python.cpp

@@ -45,6 +45,7 @@ Python::Python(LAMMPS *lmp) : Pointers(lmp)
 
 Python::~Python()
 {
+  if(pyMain) {
     // clean up
     PyGILState_STATE gstate = PyGILState_Ensure();
 
@@ -57,12 +58,13 @@ Python::~Python()
 
     // shutdown Python interpreter
 
-  if (pyMain && !external_interpreter) {
+    if (!external_interpreter) {
       Py_Finalize();
     }
     else {
       PyGILState_Release(gstate);
     }
+  }
 
   memory->sfree(pfuncs);
 }