Fix invalid fastcall dict when keywords are passed

Fixes cython#5665

I'm slightly surprised this hasn't caused more bugs. We're passing
a dict where we should be passing a tuple of names.

Replacement should hopefully be right, but I don't know how
optimized or otherwise it is.

Cython/Utility/ObjectHandling.c

@@ -2328,27 +2328,33 @@ static CYTHON_INLINE PyObject* __Pyx_PyObject_FastCallDict(PyObject *func, PyObj
     #endif
     #endif
 
-    #if CYTHON_VECTORCALL
-    #if Py_VERSION_HEX < 0x03090000
-    vectorcallfunc f = _PyVectorcall_Function(func);
-    #else
-    vectorcallfunc f = PyVectorcall_Function(func);
-    #endif
-    if (f) {
-        return f(func, args, (size_t)nargs, kwargs);
-    }
-    #elif defined(__Pyx_CyFunction_USED) && CYTHON_BACKPORT_VECTORCALL
-    // exclude fused functions for now
-    if (__Pyx_CyFunction_CheckExact(func)) {
-        __pyx_vectorcallfunc f = __Pyx_CyFunction_func_vectorcall(func);
-        if (f) return f(func, args, (size_t)nargs, kwargs);
+    if (kwargs == NULL) {
+        #if CYTHON_VECTORCALL
+        #if Py_VERSION_HEX < 0x03090000
+        vectorcallfunc f = _PyVectorcall_Function(func);
+        #else
+        vectorcallfunc f = PyVectorcall_Function(func);
+        #endif
+        if (f) {
+            return f(func, args, (size_t)nargs, NULL);
+        }
+        #elif defined(__Pyx_CyFunction_USED) && CYTHON_BACKPORT_VECTORCALL
+        // exclude fused functions for now
+        if (__Pyx_CyFunction_CheckExact(func)) {
+            __pyx_vectorcallfunc f = __Pyx_CyFunction_func_vectorcall(func);
+            if (f) return f(func, args, (size_t)nargs, NULL);
+        }
+        #endif
     }
-    #endif
 
     if (nargs == 0) {
         return __Pyx_PyObject_Call(func, $empty_tuple, kwargs);
     }
+    #if PY_VERSION_HEX >= 0x03090000 && !CYTHON_COMPILING_IN_LIMITED_API
+    return PyObject_VectorcallDict(func, args, nargs, kwargs);
+    #else
     return __Pyx_PyObject_FastCall_fallback(func, args, (size_t)nargs, kwargs);
+    #endif
 }