Narrowed is fail when use as `T` #36613

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TypeScript Version: 3.7.x-dev.201xxxxx

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export type IGunEpubNode = {
	timestamp: number,
	exists: false,
} | {
	timestamp: number,
	exists: true,

	filename: string,
	base64: string,
}

this will fail

 Error:(12, 10) TS2339: Property 'base64' does not exist on type 'IGunEpubNode'.
Error:(12, 18) TS2339: Property 'filename' does not exist on type 'IGunEpubNode'.

export function checkGunData<T extends IGunEpubNode>(data: T)
{
	if (data && data.timestamp)
	{
		if (data.exists)
		{
			let { base64, filename, exists, timestamp } = data;

			return true;
		}
	}

	return null;
}

this will work

checkGunData(data: IGunEpubNode)

Expected behavior:

both code should narrowed

checkGunData<T extends IGunEpubNode>(data: T)
checkGunData(data: IGunEpubNode)

Actual behavior:

this failed

checkGunData<T extends IGunEpubNode>(data: T)

Playground Link: http://www.typescriptlang.org/play/#code/KYDwDg9gTgLgBDAnmYcCSBxArgOwKJhYBGAchACaoC8cA3gLABQAkDAJYC2wAzjAIYcwALjg4sHIsCgAaJs1Bte3EQDM+AG27BZjAL5wAPnTnsuvAcNHjJMuQqUiYULNqZyVbdcBwDgI3lBsOADmOsxEfFoAbAAs-k5BoUy6boygkLBwKrgAxuwQOHA5ABbAOQDW2DgAInz8ADwAKnCgMN7k3OhVBMRklAB8ABTkdXwijQCUTAwsbCpww6NwAGTLcCP8AHSmPPyCUywzzMxzCxt8m-Yw3AfHR8de8LRwEdEx0lme3r4fV9wfO3Mgjg+ho5wA3KljswoMAYFgoIUnC5ISxmCkWBi5LD4YirOp1KjdEA

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