Review fixes: a missed passphrase change follows at the next backup, a key from before 1.1.0 counts as used, schedules edited in their own time zone

- A location that a passphrase change could not reach gets it at its next backup
- A key from before 1.1.0 is never replaced as an unused one
- An unreadable settings file on a location is told apart from a missing one
- A schedule is shown and saved in the zone it was saved in
- Saving an unchanged schedule keeps its moment; --timezone needs a schedule
- Schedule coverage uses the time the backup began reading its data
- Tests: catch-up scenario, upgrade test restores the new file, autumn clock change

lib/BackgroundJob/BackupJob.php

@@ -116,7 +116,7 @@ final class BackupJob extends TimedJob {
 			}
 			$attempts = $this->runs->startedSince($t->getId(), BackupService::KIND_FULL, $moment);
 			if (!\OCA\NgBackup\Service\LocationSchedule::isDue($moment, (int)$t->getScheduleSince(),
-				$this->runs->lastFinished($t->getId(), BackupService::KIND_FULL)?->getStartedAt(),
+				$this->dataStarted($this->runs->lastFinished($t->getId(), BackupService::KIND_FULL)),
 				count($attempts), ($attempts[0] ?? null)?->getFinishedAt(), $now)) {
 				continue;
 			}
@@ -127,4 +127,15 @@ final class BackupJob extends TimedJob {
 			}
 		}
 	}
+
+	/** When a backup began reading its data: a queued one can start well after it was asked for. */
+	private function dataStarted(?\OCA\NgBackup\Db\Run $run): ?int {
+		if ($run === null) {
+			return null;
+		}
+		$state = json_decode($run->getState(), true);
+		$started = is_array($state) ? ($state['files']['started'] ?? null) : null;
+		$at = is_string($started) ? strtotime($started) : false;
+		return $at !== false ? $at : $run->getStartedAt();
+	}
 }