fix seg err

Author: NyanFisher

src/msgspec/_core.c

@@ -11874,6 +11874,7 @@ quantize_decimal_obj(EncoderState *self, PyObject *obj)
     switch (self->decimal_rounding) {
         case ROUND_DEFAULT:
             rounding_const_obj = Py_None;
+            Py_INCREF(rounding_const_obj);
             break;
         case ROUND_DOWN:
             rounding_const_obj = PyUnicode_InternFromString("ROUND_DOWN");
@@ -11918,7 +11919,7 @@ quantize_decimal_obj(EncoderState *self, PyObject *obj)
     );
 
     Py_DECREF(quantize_method);
-    Py_DECREF(rounding_const_obj);
+    Py_XDECREF(rounding_const_obj);
 
     if (quantized_obj == NULL) {
         return NULL;
@@ -13537,13 +13538,13 @@ mpack_encode_decimal(EncoderState *self, PyObject *obj)
     }
 
     if (MS_LIKELY(self->decimal_format == DECIMAL_FORMAT_STRING)) {
-        temp = (quantize_obj != NULL) ? PyObject_Str(quantize_obj) : PyObject_Str(obj);
+        temp = MS_LIKELY(quantize_obj == NULL) ? PyObject_Str(obj) : PyObject_Str(quantize_obj);
         Py_XDECREF(quantize_obj);
         if (temp == NULL) return -1;
         out = mpack_encode_str(self, temp);
     }
     else {
-        temp = (quantize_obj != NULL) ? PyNumber_Float(quantize_obj) : PyNumber_Float(obj);
+        temp = MS_LIKELY(quantize_obj == NULL) ? PyNumber_Float(obj) : PyNumber_Float(quantize_obj);
         Py_XDECREF(quantize_obj);
         if (temp == NULL) return -1;
         out = mpack_encode_float(self, temp);
@@ -14198,16 +14199,13 @@ json_encode_decimal(EncoderState *self, PyObject *obj)
 {
     PyObject *temp = NULL;
 
-    if (self->decimal_quantize != NULL) {
+    if (MS_LIKELY(self->decimal_quantize == NULL)) {
+        temp = PyObject_Str(obj);
+    } else {
         PyObject *quantize_obj = quantize_decimal_obj(self, obj);
-
         if (quantize_obj == NULL) return -1;
-
         temp = PyObject_Str(quantize_obj);
-
         Py_DECREF(quantize_obj);
-    } else {
-        temp = PyObject_Str(obj);
     }
 
     if (temp == NULL) return -1;