fix: throw exception when has none collapse-panel in default slot (#1116)

components/vc-collapse/src/Collapse.jsx

@@ -70,6 +70,7 @@ export default {
       const activeKey = this.stateActiveKey;
       const { prefixCls, accordion, destroyInactivePanel, expandIcon } = this.$props;
       const newChildren = [];
+      if (this.$slots.default) {
         this.$slots.default.forEach((child, index) => {
           if (isEmptyElement(child)) return;
           const { header, headerClass, disabled } = getPropsData(child);
@@ -108,6 +109,7 @@ export default {
 
           newChildren.push(cloneElement(child, props));
         });
+      }
       return newChildren;
     },
     setActiveKey(activeKey) {