bpo-38304: Fix PyConfig usage in python_uwp.cpp (GH-16487)

* Set PyPreConfig.struct_size and PyConfig.struct_size as required by
  the API.
* PyPreConfig_InitPythonConfig() can now fail: check PyStatus result.
diff --git a/PC/python_uwp.cpp b/PC/python_uwp.cpp
index 06c1dd3..2656d18 100644
--- a/PC/python_uwp.cpp
+++ b/PC/python_uwp.cpp
@@ -167,7 +167,10 @@
     PyStatus status;
 
     PyPreConfig preconfig;
+    preconfig.struct_size = sizeof(PyPreConfig);
+
     PyConfig config;
+    config.struct_size = sizeof(PyConfig);
 
     const wchar_t *moduleName = NULL;
     const wchar_t *p = wcsrchr(argv[0], L'\\');
@@ -186,7 +189,10 @@
         }
     }
 
-    PyPreConfig_InitPythonConfig(&preconfig);
+    status = PyPreConfig_InitPythonConfig(&preconfig);
+    if (PyStatus_Exception(status)) {
+        goto fail_without_config;
+    }
     if (!moduleName) {
         status = Py_PreInitializeFromArgs(&preconfig, argc, argv);
         if (PyStatus_Exception(status)) {