Avoid mailing users that have explicitly unwatched an issue (#10475)

[6543]

backports #10475

[6543]

@guillep2k done

[strk]

I understand this is a backport so LGTM (just to move things further) but it doesn't seem clean to call that getIssuesWatchers twice, rather I'd expect such a function to internally remove explicit unsubscribers...

[6543]

@strk it doesnt work that way ... since you can "watch" via repo watch or participants or issuewatch ... and there are 3 types of issuewatch:

• 1. No entry in table (so it use default witch is not subscribed unless you watch the repo or have participated)
• 2. IssueWatch.IsWatching = true; explicit watch
• 3. IssueWatch.IsWatching = false; explicit DONT watch

So i can query the userIDs in two functioncalls or query all IssueWatch entrys for a issue and itterate throu it fo set / unset ...