Fix incorrect initial tabs position for vertical tab bars

Summary:
This fixes the incorrect initial positioning of the tabs for vertical
tab bars that persisted until the user switched to another tab
manually.

BUG: 395390
FIXED-IN: 5.62

Reviewers: #plasma, ngraham, hein

Reviewed By: #plasma, ngraham, hein

Subscribers: kde-frameworks-devel

Tags: #frameworks

Maniphest Tasks: T10047

Differential Revision: https://phabricator.kde.org/D23036

src/declarativeimports/plasmacomponents/qml/TabBar.qml

@@ -171,7 +171,11 @@ FocusScope {
         }
     }
 
-    onCurrentTabChanged: {
+    onCurrentTabChanged: updateTabPosition()
+    onWidthChanged: updateTabPosition()
+    onHeightChanged: updateTabPosition()
+
+    function updateTabPosition() {
         if (!currentTab) {
             return;
         }
@@ -182,16 +186,6 @@ FocusScope {
         }
     }
 
-    onWidthChanged: {
-        if (currentTab) {
-            if (layout.isHorizontal) {
-                tabBarLayout.x = Math.max(Math.min(0, -(currentTab.x + currentTab.width/2) + tabbarScroller.width/2), -tabBarLayout.width + tabbarScroller.width);
-            } else {
-                tabBarLayout.y = Math.max(Math.min(0, -(currentTab.y + currentTab.height/2) + tabbarScroller.height/2), -tabBarLayout.height + tabbarScroller.height);
-            }
-        }
-    }
-
     Item {
         id: tabbarScroller
         clip: true