Revert pre-size and empty fast path in lazy modules snapshot

Drop _PyDict_NewPresized and the empty-registry short-circuit. Both
were micro-optimizations with negligible impact for typical registry
sizes; the simpler unconditional PyDict_New + iterate path is easier
to read.

Author: johnslavik

Python/import.c

@@ -290,44 +290,34 @@ _PyImport_GetLazyModulesSnapshot(PyInterpreterState *interp)
         return PyFrozenDict_New(NULL);
     }
 
-    PyObject *tmp = NULL;
-    int err = 0;
+    PyObject *tmp = PyDict_New();
+    if (tmp == NULL) {
+        return NULL;
+    }
 
+    int err = 0;
     Py_BEGIN_CRITICAL_SECTION(lazy_modules);
-    Py_ssize_t size = PyDict_GET_SIZE(lazy_modules);
-    if (size > 0) {
-        tmp = _PyDict_NewPresized(size);
-        if (tmp == NULL) {
+    Py_ssize_t pos = 0;
+    PyObject *key, *value;
+    while (PyDict_Next(lazy_modules, &pos, &key, &value)) {
+        PyObject *frozen = PyFrozenSet_New(value);
+        if (frozen == NULL) {
             err = -1;
+            break;
         }
-        else {
-            Py_ssize_t pos = 0;
-            PyObject *key, *value;
-            while (PyDict_Next(lazy_modules, &pos, &key, &value)) {
-                PyObject *frozen = PyFrozenSet_New(value);
-                if (frozen == NULL) {
-                    err = -1;
-                    break;
-                }
-                if (PyDict_SetItem(tmp, key, frozen) < 0) {
-                    Py_DECREF(frozen);
-                    err = -1;
-                    break;
-                }
-                Py_DECREF(frozen);
-            }
+        if (PyDict_SetItem(tmp, key, frozen) < 0) {
+            Py_DECREF(frozen);
+            err = -1;
+            break;
         }
+        Py_DECREF(frozen);
     }
     Py_END_CRITICAL_SECTION();
 
     if (err < 0) {
-        Py_XDECREF(tmp);
+        Py_DECREF(tmp);
         return NULL;
     }
-    if (tmp == NULL) {
-        // Registry is empty.
-        return PyFrozenDict_New(NULL);
-    }
 
     PyObject *snapshot = PyFrozenDict_New(tmp);
     Py_DECREF(tmp);