Don't allow deleting items when a spacer move operation is running.

BUG: 408434

src/timeline2/view/qml/timeline.qml

@@ -13,7 +13,7 @@ Rectangle {
     property bool validMenu: false
     property color textColor: activePalette.text
     property var groupTrimData
-    property bool dragInProgress: dragProxyArea.pressed || dragProxyArea.drag.active || groupTrimData !== undefined
+    property bool dragInProgress: dragProxyArea.pressed || dragProxyArea.drag.active || groupTrimData !== undefined || spacerGroup > -1
 
     signal clipClicked()
     signal mousePosChanged(int position)

src/timeline2/view/timelinecontroller.cpp

@@ -501,6 +501,11 @@ int TimelineController::insertComposition(int tid, int position, const QString &
 
 void TimelineController::deleteSelectedClips()
 {
+    if (dragOperationRunning()) {
+        // Don't allow timeline operation while drag in progress
+        pCore->displayMessage(i18n("Cannot perform operation while dragging in timeline"), ErrorMessage);
+        return;
+    }
     auto sel = m_model->getCurrentSelection();
     if (sel.empty()) {
         // Check if a mix is selected