Fix missing/incomplete NULL checks in multiple source files

Modules/_zoneinfo.c

@@ -2572,6 +2572,9 @@ update_strong_cache(zoneinfo_state *state, const PyTypeObject *const type,
     }
 
     StrongCacheNode *new_node = strong_cache_node_new(key, zone);
+    if (new_node == NULL) {
+        return;
+    }
     StrongCacheNode **root = &(state->ZONEINFO_STRONG_CACHE);
     move_strong_cache_node_to_front(state, root, new_node);
 

Modules/errnomodule.c

@@ -84,6 +84,7 @@ errno_exec(PyObject *module)
     PyObject *module_dict = PyModule_GetDict(module);
     PyObject *error_dict = PyDict_New();
     if (!module_dict || !error_dict) {
+        Py_XDECREF(error_dict);
         return -1;
     }
     if (PyDict_SetItemString(module_dict, "errorcode", error_dict) < 0) {

Modules/posixmodule.c

@@ -9023,6 +9023,10 @@ os_setgroups(PyObject *module, PyObject *groups)
     }
 
     gid_t *grouplist = PyMem_New(gid_t, len);
+    if (grouplist == NULL) {
+        PyErr_NoMemory();
+        return NULL;
+    }
     for (Py_ssize_t i = 0; i < len; i++) {
         PyObject *elem;
         elem = PySequence_GetItem(groups, i);

Modules/sha1module.c

@@ -71,6 +71,9 @@ static SHA1object *
 newSHA1object(SHA1State *st)
 {
     SHA1object *sha = (SHA1object *)PyObject_GC_New(SHA1object, st->sha1_type);
+    if (sha == NULL) {
+        return NULL;
+    }
     PyObject_GC_Track(sha);
     return sha;
 }

Modules/zlibmodule.c

@@ -1722,6 +1722,9 @@ ZlibDecompressor__new__(PyTypeObject *cls,
         return NULL;
     }
     ZlibDecompressor *self = PyObject_New(ZlibDecompressor, cls);
+    if (self == NULL) {
+        return NULL;
+    }
     self->eof = 0;
     self->needs_input = 1;
     self->avail_in_real = 0;