Can't watch age restricted video

[Velava67]

Checklist

• I am using the latest version - 0.21.5
• I checked, but didn't find any duplicates (open OR closed) of this issue in the repo.
• I have read the contribution guidelines given at https://github.com/TeamNewPipe/NewPipe/blob/HEAD/.github/CONTRIBUTING.md.
• This issue contains only one bug. I will open one issue for every bug report I want to file.

Steps to reproduce the bug

1. Try to open https://m.youtube.com/watch?v=G4wt-4Bx3Cg

Actual behaviour

I got this when a try to watch something with age restriction "Sorry, something went wrong"

Expected behavior

Screenshots/Screen recordings

Logs

Exception

• User Action: requested stream
• Request: https://www.youtube.com/watch?v=G4wt-4Bx3Cg
• Content Country: US
• Content Language: en
• App Language: en
• Service: YouTube
• Version: 0.21.5
• OS: Linux Android 7.0 - 24

Crash log

java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.String.length()' on a null object reference
	at java.io.StringReader.<init>(StringReader.java:50)
	at com.grack.nanojson.JsonParser$JsonParserContext.from(Unknown Source)
	at org.schabi.newpipe.extractor.services.youtube.extractors.YoutubeStreamExtractor.fetchVideoInfoPage(YoutubeStreamExtractor.java:802)
	at org.schabi.newpipe.extractor.services.youtube.extractors.YoutubeStreamExtractor.onFetchPage(YoutubeStreamExtractor.java:731)
	at org.schabi.newpipe.extractor.Extractor.fetchPage(Extractor.java:54)
	at org.schabi.newpipe.extractor.stream.StreamInfo.getInfo(StreamInfo.java:68)
	at org.schabi.newpipe.extractor.stream.StreamInfo.getInfo(StreamInfo.java:64)
	at org.schabi.newpipe.util.ExtractorHelper.lambda$getStreamInfo$3(ExtractorHelper.java:115)
	at org.schabi.newpipe.util.-$$Lambda$ExtractorHelper$YTHJjScxCJNO1LTCqs3IKy35iyY.call(lambda)
	at io.reactivex.rxjava3.internal.operators.single.SingleFromCallable.subscribeActual(SingleFromCallable.java:43)
	at io.reactivex.rxjava3.core.Single.subscribe(Single.java:4813)
	at io.reactivex.rxjava3.internal.operators.single.SingleDoOnSuccess.subscribeActual(SingleDoOnSuccess.java:35)
	at io.reactivex.rxjava3.core.Single.subscribe(Single.java:4813)
	at io.reactivex.rxjava3.internal.operators.single.SingleSubscribeOn$SubscribeOnObserver.run(SingleSubscribeOn.java:89)
	at io.reactivex.rxjava3.core.Scheduler$DisposeTask.run(Scheduler.java:614)
	at io.reactivex.rxjava3.internal.schedulers.ScheduledRunnable.run(ScheduledRunnable.java:65)
	at io.reactivex.rxjava3.internal.schedulers.ScheduledRunnable.call(ScheduledRunnable.java:56)
	at java.util.concurrent.FutureTask.run(FutureTask.java:237)
	at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:272)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1133)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:607)
	at java.lang.Thread.run(Thread.java:761)

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[SameenAhnaf]

Duplicate of #6403.