Improve the behaviour of jump to last unread message.

Improve the behaviour of jump to last unread message. The view will now jump as high as possible if the last unread message isn't loaded. This at least triggers more items to load which will eventually get the user to the last unread message.

src/qml/TimelineView.qml

@@ -190,12 +190,15 @@ QQC2.ScrollView {
             implicitHeight: Kirigami.Units.gridUnit * 2
 
             z: 2
-            visible: root.currentRoom && root.currentRoom.hasUnreadMessages && root.currentRoom.readMarkerLoaded
+            visible: root.currentRoom && root.currentRoom.hasUnreadMessages
+
+            text: root.currentRoom.readMarkerLoaded ? i18n("Jump to first unread message") : i18n("Jump to oldest loaded message")
             action: Kirigami.Action {
                 onTriggered: {
                     if (!Kirigami.Settings.isMobile) {
                         root.focusChatBar();
                     }
+                    goReadMarkerFab.textChanged()
                     messageListView.goToEvent(root.currentRoom.readMarkerEventId);
                 }
                 icon.name: "go-up"
@@ -203,7 +206,10 @@ QQC2.ScrollView {
             }
 
             QQC2.ToolTip {
-                text: i18n("Jump to first unread message")
+                id: goReadMarkerFabTooltip
+                text: goReadMarkerFab.text
+                delay: Kirigami.Units.toolTipDelay
+                visible: goReadMarkerFab.hovered
             }
         }
         KirigamiComponents.FloatingButton {
@@ -274,6 +280,10 @@ QQC2.ScrollView {
 
         function goToEvent(eventID) {
             const index = eventToIndex(eventID);
+            if (index == -1) {
+                messageListView.positionViewAtEnd();
+                return;
+            }
             messageListView.positionViewAtIndex(index, ListView.Center);
             itemAtIndex(index).isTemporaryHighlighted = true;
         }