bad remote bug URL cause OOPSes in Mantis.initializeRemoteBugDB()

[Abel Deuring]

The remote bug URL (https://bugtrack.alsa-project.org/alsa-bug/view.php?id=4163]) specified here:
https://bugs.edge.launchpad.net/bugs/278648/+watch/65624 contains a typo (the trailing ']') and leads to an OOPS in Mantis.initializeRemoteBugDB(), thus preventing the update of other bug watches from this tracker.

We should simply label such a bug watch as "invaild".

Since we rely on user input for bug watch URLs, we should even perhaps "expect" such mistakes and try to access the remote bug when a bug watch is created or changed. This would also allow us to show the user a confirmation page like "This is the remote bug: title: .... Severity: ...., Status: ..... Is this the remote bug you want to link? (yes/no)"