fix #28: menu items invisible after 1.8.4

appinfo/info.xml

@@ -17,7 +17,7 @@ You can report a bug or request a feature by opening an issue.
 ]]></description>
     <licence>agpl</licence>
     <author mail="contact@deblan.fr" homepage="https://www.deblan.io/">Simon Vieille</author>
-    <version>1.8.3</version>
+    <version>1.8.5</version>
     <namespace>SideMenu</namespace>
     <category>customization</category>
     <website>https://gitnet.fr/deblan/side_menu</website>
@@ -30,7 +30,7 @@ You can report a bug or request a feature by opening an issue.
     <screenshot>https://upload.deblan.org/u/2020-08/5f35aae1.png</screenshot>
     <screenshot>https://upload.deblan.org/u/2020-08/5f35ab0f.png</screenshot>
     <dependencies>
-        <nextcloud min-version="18" max-version="19"/>
+        <nextcloud min-version="18" max-version="20"/>
     </dependencies>
 	<settings>
 		<admin>OCA\SideMenu\Settings\Admin</admin>

src/SideMenu.vue

@@ -52,8 +52,11 @@ export default {
             this.apps = []
             const links = document.querySelectorAll('#appmenu a')
             const menu = document.querySelector('#appmenu')
+            let menuIsHidden = true
 
-            const menuIsHidden = window.getComputedStyle(menu, null).getPropertyValue('display') === 'none';
+            if (menu) {
+                menuIsHidden = window.getComputedStyle(menu, null).getPropertyValue('display') === 'none'
+            }
 
             for (let element of links) {
                 let href = element.getAttribute('href')