SLI-1521 TreeUI should be accessed only from EDT

src/main/java/org/sonarlint/intellij/ui/AbstractIssuesPanel.java

@@ -26,6 +26,7 @@
 import com.intellij.openapi.actionSystem.ActionToolbar;
 import com.intellij.openapi.actionSystem.AnAction;
 import com.intellij.openapi.actionSystem.DefaultActionGroup;
+import com.intellij.openapi.application.ApplicationManager;
 import com.intellij.openapi.fileEditor.OpenFileDescriptor;
 import com.intellij.openapi.project.Project;
 import com.intellij.openapi.ui.SimpleToolWindowPanel;
@@ -188,13 +189,17 @@ private OccurenceNavigator.OccurenceInfo occurrence(Tree tree, @Nullable IssueNo
   @Override
   public boolean hasNextOccurence() {
     // relies on the assumption that a TreeNodes will always be the last row in the table view of the tree
-    var isOldTree = tree.getSelectionPath() == null;
-    var path = isOldTree ? oldTree.getSelectionPath() : tree.getSelectionPath();
-    if (path == null) {
-      return false;
-    }
-
-    return isOldTree ? fetchNextOccurenceInfo(path, oldTree) : fetchNextOccurenceInfo(path, tree);
+    var result = new boolean[1];
+    ApplicationManager.getApplication().invokeAndWait(() -> {
+      var isOldTree = tree.getSelectionPath() == null;
+      var path = isOldTree ? oldTree.getSelectionPath() : tree.getSelectionPath();
+      if (path == null) {
+        result[0] = false;
+      } else {
+        result[0] = isOldTree ? fetchNextOccurenceInfo(path, oldTree) : fetchNextOccurenceInfo(path, tree);
+      }
+    });
+    return result[0];
   }
 
   private static boolean fetchNextOccurenceInfo(TreePath path, Tree tree) {