Correctly set the "firstExecutionTime" of a "HATask"

In case an initial delay is used for "Timer::scheduleAtFixedRate" (e.g. when rescheduling) then the "firstExecutionTime" of the "HATask" was incorrect, since it considered the first execution to be based on the actual interval.
This caused
 - calculations for execution times (e.g. "timeToNextExecution", "nextExecutionTime") to be incorrect
 - the ordering of the "scheduledTasks" queue to be incorrect

server/src/main/kotlin/suwayomi/tachidesk/util/HAScheduler.kt

@@ -48,8 +48,8 @@ class HACronTask(id: String, val cronExpr: String, execute: () -> Unit, name: St
     }
 }
 
-class HATask(id: String, val interval: Long, execute: () -> Unit, val timerTask: TimerTask, name: String?) : BaseHATask(id, execute, name) {
-    private val firstExecutionTime = System.currentTimeMillis() + interval
+class HATask(id: String, val interval: Long, execute: () -> Unit, val timerTask: TimerTask, name: String?, initialDelay: Long = interval) : BaseHATask(id, execute, name) {
+    private val firstExecutionTime = System.currentTimeMillis() + initialDelay
 
     private fun getElapsedTimeOfCurrentInterval(): Long {
         val timeSinceFirstExecution = System.currentTimeMillis() - firstExecutionTime
@@ -179,7 +179,7 @@ object HAScheduler {
         val intervalDifference = interval - task.interval
         val remainingTimeTillNextExecution = (timeToNextExecution + intervalDifference).coerceAtLeast(0)
 
-        scheduledTasks.add(HATask(taskId, interval, task.execute, timerTask, task.name))
+        scheduledTasks.add(HATask(taskId, interval, task.execute, timerTask, task.name, initialDelay = remainingTimeTillNextExecution))
         timer.scheduleAtFixedRate(timerTask, remainingTimeTillNextExecution, interval)
     }