[YouTube] Fix getting the comment text if the comment contains a hashtag

[TobiGr]

• I carefully read the contribution guidelines and agree to them.
• I have tested the API against NewPipe.
• I agree to create a pull request for NewPipe as soon as possible to make it compatible with the changed API.

This fix needs further investigation.
The current approach is very strict and throws a ParsingException if the webCommandMetadata is present, but no URL field is given. I was not able to find any other occurrences of that field, but that does not mean there aren't any (I don't know much about the navigationEndpoint, maybe somebody can help us out here). A possibly better solution is to put the condition before the if () else if ... block as shown below to prevent any unintentional exceptions.

@Nullable
public static String getUrlFromNavigationEndpoint(@Nonnull final JsonObject navigationEndpoint)
        throws ParsingException {
   if (navigationEndpoint.has("webCommandMetadata")) {
        // this case needs to be handled before the browseEndpoint,
        // e.g. for hashtags in comments
        final JsonObject metadata = navigationEndpoint.getObject("webCommandMetadata");
        if (metadata.has("url")) {
            return "https://www.youtube.com" + metadata.getString("url");
        }
    }
    if (navigationEndpoint.has("urlEndpoint")) {
        // ...
    } else if (navigationEndpoint.has("browseEndpoint")) {
    // ...

Fixes #1019

[Stypox]

I think the solution you propose in the PR body is better. In the end, I don't think anything could go wrong if webCommandMetadata is actually supposed to appear when the other two aren't there. But if this wasn't actually the case, we would be more future-proof.