Share to Android: After sharing once, app opened to "share" screen on startup the next few times

[chrisbobbe]

@timabbott reports that, after sharing to Zulip once, the next few times he opened the app, it had him on the "share" screen. More discussion in chat.

I just looked at the code, and I don't have a specific diagnosis yet.

I don't think it's a problem with how we're organizing our React Navigation screens; I can say more about this.

I think we're immediately navigating to the sharing screen, from some other initial screen, when we shouldn't be.

I don't know if the navigation is happening because of an "initial share" (await Sharing.readInitialSharedContent() being non-null) or because of a 'shareReceived' event.

I suspect the app might be receiving the share intent multiple times, and we should only be handling it the first time. Could it be some other flavor of 70e9ad9? The relevant code there was refactored in 1a20529; could there have been an issue there? Neither of those commits were released very recently.