ZP-1355 Make sure the impersonated username is always lowercase.

Released under the Affero GNU General
Public License (AGPL) version 3.

src/backend/kopano/kopano.php

@@ -144,7 +144,7 @@ class BackendKopano implements IBackend, ISearchProvider {
 
         $this->mainUser = strtolower($user);
         // TODO the impersonated user should be passed directly to IBackend->Logon() - ZP-1351
-        $this->impersonateUser = Request::GetImpersonatedUser();
+        $this->impersonateUser = strtolower(Request::GetImpersonatedUser());
 
         // check if we are impersonating someone
         // $defaultUser will be used for $this->defaultStore