fix(dropzone): move guard before accepted event dispatch

Author: cdransf

2nd-gen/packages/core/components/dropzone/Dropzone.base.ts

@@ -143,6 +143,10 @@ export abstract class DropzoneBase extends SizedMixin(SpectrumElement, {
   private readonly _onDragOver = (event: DragEvent): void => {
     event.preventDefault();
 
+    if (!event.dataTransfer) {
+      return;
+    }
+
     const shouldAcceptEvent = new CustomEvent<DragEvent>(
       SWC_DROPZONE_SHOULD_ACCEPT_EVENT,
       {
@@ -155,10 +159,6 @@ export abstract class DropzoneBase extends SizedMixin(SpectrumElement, {
 
     const accepted = this.dispatchEvent(shouldAcceptEvent);
 
-    if (!event.dataTransfer) {
-      return;
-    }
-
     if (!accepted) {
       event.dataTransfer.dropEffect = 'none';
       return;