Focus center event if scrolled up when ctrl+j/k

When using the focus(Previous/Next)Message keybinds, no message is
focused and the view has been scrolled up, focus the message in the
center of the view instead of returning to the list's bottom to focus
the most recent one.

src/gui/Pages/Chat/Timeline/EventList.qml

@@ -26,15 +26,12 @@ Rectangle {
 
     HShortcut {
         sequences: window.settings.keys.focusPreviousMessage
-        onActivated: eventList.incrementCurrentIndex()
+        onActivated: eventList.focusPreviousMessage()
     }
 
     HShortcut {
         sequences: window.settings.keys.focusNextMessage
-        onActivated:
-            eventList.currentIndex === 0 ?
-            eventList.currentIndex = -1 :
-            eventList.decrementCurrentIndex()
+        onActivated: eventList.focusNextMessage()
     }
 
     HShortcut {
@@ -244,6 +241,29 @@ Rectangle {
         readonly property var redactableCheckedEvents:
             getSortedChecked().filter(ev => eventList.canRedact(ev))
 
+        function focusCenterMessage() {
+            const previous     = highlightRangeMode
+            highlightRangeMode = HListView.NoHighlightRange
+            currentIndex       = indexAt(0, contentY + height / 2)
+            highlightRangeMode = previous
+        }
+
+        function focusPreviousMessage() {
+            currentIndex === -1 && contentY < -height - bottomMargin * 2 ?
+            focusCenterMessage() :
+            incrementCurrentIndex()
+        }
+
+        function focusNextMessage() {
+            currentIndex === -1 && contentY <= -height - bottomMargin * 2 ?
+            focusCenterMessage() :
+
+            eventList.currentIndex === 0 ?
+            eventList.currentIndex = -1 :
+
+            decrementCurrentIndex()
+        }
+
         function copySelectedDelegates() {
             if (eventList.selectedText) {
                 Clipboard.text = eventList.selectedText