Fix the issue where selecting another operator was not possible after…

… deleting a selected operator in the workspace (#3284)

### Purpose:
Currently, after deleting an operator with detail buttons open,
attempting to open the detail buttons of another operator results in a
missing attr issue. The root cause is that the previous implementation
did not account for the attr disappearing after the operator was
deleted.

### Changes:
Add a check for currentOpenOperatorId; if the ID does not exist, no
operation will be performed.

### Demos:
Before:


https://github.com/user-attachments/assets/a1f325db-f14a-42fd-a022-79c4e2e0129e


After:


https://github.com/user-attachments/assets/1338fa11-989a-4ee4-8b48-02ccc02a82a8

core/gui/src/app/workspace/component/workflow-editor/workflow-editor.component.ts

@@ -758,30 +758,35 @@ export class WorkflowEditorComponent implements AfterViewInit, OnDestroy {
     fromJointPaperEvent(this.paper, "element:pointerdown")
       .pipe(untilDestroyed(this))
       .subscribe(event => {
-        if (this.currentOpenedOperatorID !== null) {
+        const operatorID = event[0].model.id.toString();
+
+        if (this.currentOpenedOperatorID !== null && this.paper.getModelById(this.currentOpenedOperatorID)) {
           this.jointUIService.foldOperatorDetails(this.paper, this.currentOpenedOperatorID);
         }
 
-        this.currentOpenedOperatorID = event[0].model.id.toString();
-        this.jointUIService.unfoldOperatorDetails(this.paper, this.currentOpenedOperatorID);
+        this.currentOpenedOperatorID = operatorID;
+        this.jointUIService.unfoldOperatorDetails(this.paper, operatorID);
       });
 
     fromJointPaperEvent(this.paper, "element:contextmenu")
       .pipe(untilDestroyed(this))
       .subscribe(event => {
-        if (this.currentOpenedOperatorID !== null) {
+        const operatorID = event[0].model.id.toString();
+
+        if (this.currentOpenedOperatorID !== null && this.paper.getModelById(this.currentOpenedOperatorID)) {
           this.jointUIService.foldOperatorDetails(this.paper, this.currentOpenedOperatorID);
         }
 
-        this.currentOpenedOperatorID = event[0].model.id.toString();
-        this.jointUIService.unfoldOperatorDetails(this.paper, event[0].model.id.toString());
+        this.currentOpenedOperatorID = operatorID;
+        this.jointUIService.unfoldOperatorDetails(this.paper, operatorID);
       });
 
     fromJointPaperEvent(this.paper, "blank:pointerdown")
       .pipe(untilDestroyed(this))
       .subscribe(() => {
-        if (this.currentOpenedOperatorID !== null) {
+        if (this.currentOpenedOperatorID !== null && this.paper.getModelById(this.currentOpenedOperatorID)) {
           this.jointUIService.foldOperatorDetails(this.paper, this.currentOpenedOperatorID);
+          this.currentOpenedOperatorID = null;
         }
       });
   }