[PYTHON] Allow no de-allocation when exit (#583)

python/tvm/_ffi/_ctypes/ndarray.py

@@ -22,7 +22,7 @@ class NDArrayBase(object):
         self.is_view = is_view
 
     def __del__(self):
-        if not self.is_view:
+        if not self.is_view and _LIB:
             check_call(_LIB.TVMArrayFree(self.handle))
 
     @property