fix(vuepress-theme-reco): fix subSidebar invalid

ISSUES CLOSED: #267

Author: reco_luan

.gitignore

@@ -3,4 +3,5 @@ yarn-error.log
 .idea
 yarn.lock
 .DS_Store
+.vscode
 package-lock.json

packages/@vuepress-reco/vuepress-plugin-bulletin-popover/lib/vuepress-plugin-bulletin-popover.js

@@ -50,8 +50,15 @@ export default {
 
       const headers = this.$page.headers || []
 
-      return [themeSubSidebar, themeSidebar, pageSubSidebar, pageSidebar].indexOf('auto') > -1 &&
-             headers.length > 0
+      if ([pageSubSidebar, pageSidebar].indexOf(false) > -1) {
+        return false
+      } else if ([pageSubSidebar, pageSidebar].indexOf('auto') > -1 && headers.length > 0) {
+        return true
+      } else if ([themeSubSidebar, themeSidebar].indexOf('auto') > -1 && headers.length > 0) {
+        return true
+      } else {
+        return false
+      }
     }
   }
 }