[3.7] bpo-35373: Fix PyInit_timezone() error handling (GH-10864)

[3.7] bpo-35373: Fix PyInit_timezone() error handling (GH-10864)

* bpo-35373: Fix PyInit_timezone() error handling

PyInit_timezone() now returns -1 at exit if an exception is raised.
Check also explicitly PyUnicode_DecodeLocale() and Py_BuildValue()
errors.

* bpo-35373: Fix PyInit_time() error handling (GH-10865)

* PyInit_time() now returns NULL if an exception is raised.
* Rename PyInit_timezone() to init_timezone(). "PyInit_" prefix is
  a special prefix for function initializing a module.
  init_timezone() doesn't initialize a module and the function is not
  exported.

(cherry picked from commit 3bb150d8148e3cc08418077a58f43e064b9fde61)