Better handle return values from Filesystem::getMountBy*

getMountByStorageId and getMountByNumericId return an empty array on error,
which should be detected to avoid possible errors. This commit also adds in
some new logging points and throws to aid debugging

apps/files_sharing/lib/cache.php

@@ -54,7 +54,7 @@ class Shared_Cache extends Cache {
 		if (isset($source['path']) && isset($source['fileOwner'])) {
 			\OC\Files\Filesystem::initMountPoints($source['fileOwner']);
 			$mounts = \OC\Files\Filesystem::getMountByNumericId($source['storage']);
-			if (is_array($mounts) and count($mounts)) {
+			if (is_array($mounts) and !empty($mounts)) {
 				$fullPath = $mounts[0]->getMountPoint() . $source['path'];
 				list($storage, $internalPath) = \OC\Files\Filesystem::resolvePath($fullPath);
 				if ($storage) {

apps/files_sharing/lib/sharedstorage.php

@@ -87,10 +87,11 @@ class Shared extends \OC\Files\Storage\Common {
 			if (!isset($source['fullPath'])) {
 				\OC\Files\Filesystem::initMountPoints($source['fileOwner']);
 				$mount = \OC\Files\Filesystem::getMountByNumericId($source['storage']);
-				if (is_array($mount)) {
+				if (is_array($mount) && !empty($mount)) {
 					$this->files[$target]['fullPath'] = $mount[key($mount)]->getMountPoint() . $source['path'];
 				} else {
 					$this->files[$target]['fullPath'] = false;
+					\OCP\Util::writeLog('files_sharing', "Unable to get mount for shared storage '" . $source['storage'] . "' user '" . $source['fileOwner'] . "'", \OCP\Util::ERROR);
 				}
 			}
 			return $this->files[$target]['fullPath'];

lib/private/share/share.php

@@ -1228,7 +1228,7 @@ class Share extends \OC\Share\Constants {
 				} else {
 					if (!isset($mounts[$row['storage']])) {
 						$mountPoints = \OC\Files\Filesystem::getMountByNumericId($row['storage']);
-						if (is_array($mountPoints)) {
+						if (is_array($mountPoints) && !empty($mountPoints)) {
 							$mounts[$row['storage']] = current($mountPoints);
 						}
 					}