fix: line authoring crashes when dom Element cannot be removed. (#891)

* fix: line authoring crashes when dom Element cannot be removed.

* fix: format

Author: GollyTicker

src/lineAuthor/view/gutter/gutter.ts

@@ -55,7 +55,13 @@ export class TextGutter extends GutterMarker {
     }
 
     destroy(dom: HTMLElement): void {
-        if (!document.body.contains(dom)) dom.remove();
+        if (!dom) {
+            return; // sometimes, it doesn't exist anymore.
+        }
+
+        if (!document.body.contains(dom)) {
+            dom.remove();
+        }
     }
 }
 
@@ -115,10 +121,14 @@ export class LineAuthoringGutter extends GutterMarker {
     }
 
     public destroy(dom: HTMLElement): void {
+        if (!dom) {
+            return; // sometimes, it doesn't exist anymore.
+        }
+
         // this is called frequently, when the gutter moves outside of the view.
         if (!document.body.contains(dom)) {
-            dom.remove();
             attachedGutterElements.delete(dom);
+            dom.remove();
         }
     }