PYTHON-4663 Fix coverity warnings in datetime decoding change (#1835)

Author: ShaneHarvey

bson/_cbsonmodule.c

@@ -383,10 +383,11 @@ static int millis_from_datetime_ms(PyObject* dt, long long* out){
 static PyObject* decode_datetime(PyObject* self, long long millis, const codec_options_t* options){
     PyObject* naive = NULL;
     PyObject* replace = NULL;
-    PyObject* args = NULL;
-    PyObject* kwargs = NULL;
     PyObject* value = NULL;
     struct module_state *state = GETSTATE(self);
+    if (!state) {
+        goto invalid;
+    }
     if (options->datetime_conversion == DATETIME_MS){
         return datetime_ms_from_millis(self, millis);
     }
@@ -414,8 +415,8 @@ static PyObject* decode_datetime(PyObject* self, long long millis, const codec_o
                     Py_DECREF(utcoffset);
                     return 0;
                 }
-                min_millis_offset = (PyDateTime_DELTA_GET_DAYS(utcoffset) * 86400 +
-                                     PyDateTime_DELTA_GET_SECONDS(utcoffset)) * 1000 +
+                min_millis_offset = (PyDateTime_DELTA_GET_DAYS(utcoffset) * (int64_t)86400 +
+                                     PyDateTime_DELTA_GET_SECONDS(utcoffset)) * (int64_t)1000 +
                                      (PyDateTime_DELTA_GET_MICROSECONDS(utcoffset) / 1000);
             }
             Py_DECREF(utcoffset);
@@ -433,8 +434,8 @@ static PyObject* decode_datetime(PyObject* self, long long millis, const codec_o
                     Py_DECREF(utcoffset);
                     return 0;
                 }
-                max_millis_offset = (PyDateTime_DELTA_GET_DAYS(utcoffset) * 86400 +
-                                     PyDateTime_DELTA_GET_SECONDS(utcoffset)) * 1000 +
+                max_millis_offset = (PyDateTime_DELTA_GET_DAYS(utcoffset) * (int64_t)86400 +
+                                     PyDateTime_DELTA_GET_SECONDS(utcoffset)) * (int64_t)1000 +
                                      (PyDateTime_DELTA_GET_MICROSECONDS(utcoffset) / 1000);
             }
             Py_DECREF(utcoffset);
@@ -487,8 +488,6 @@ static PyObject* decode_datetime(PyObject* self, long long millis, const codec_o
 invalid:
     Py_XDECREF(naive);
     Py_XDECREF(replace);
-    Py_XDECREF(args);
-    Py_XDECREF(kwargs);
     return value;
 }