Fix public shared folder page when quota includes external storages

When the quota storage wrapper is used (that is, when the share owner
has a quota set) and "quota_include_external_storage" is enabled when
checking the free space "Filesystem::getFileInfo('', 'ext')" is called,
which requires the file system to have been initialized. This is
explicitly done now in "showShare" similar to what is done in
"downloadShare".

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>

apps/files_sharing/lib/Controller/ShareController.php

@@ -403,6 +403,13 @@ public function showShare($path = ''): TemplateResponse {
 
 			$shareTmpl['dir'] = $shareNode->getRelativePath($folderNode->getPath());
 
+			// In some cases (for example, when quota includes the external
+			// storages) the filesystem needs to be mounted to be able to check
+			// the free space.
+			/* FIXME: We should do this all nicely in OCP */
+			OC_Util::tearDownFS();
+			OC_Util::setupFS($share->getShareOwner());
+
 			/*
 			 * The OC_Util methods require a view. This just uses the node API
 			 */