fix: handle case where we can't get the filesize after open in dav get

Signed-off-by: Robin Appelman <robin@icewind.nl>

Author: icewind1991

apps/dav/lib/Connector/Sabre/File.php

@@ -474,11 +474,15 @@ public function get() {
 				}
 			}
 
+			$logger = Server::get(LoggerInterface::class);
 			// comparing current file size with the one in DB
 			// if different, fix DB and refresh cache.
+			//
 			$fsSize = $this->fileView->filesize($this->getPath());
-			if ($this->getSize() !== $fsSize) {
-				$logger = Server::get(LoggerInterface::class);
+			if ($fsSize === false) {
+				$logger->warning('file not found on storage after successfully opening it');
+				throw new ServiceUnavailable($this->l10n->t('Failed to get size for : %1$s', [$this->getPath()]));
+			} elseif ($this->getSize() !== $fsSize) {
 				$logger->warning('fixing cached size of file id=' . $this->getId() . ', cached size was ' . $this->getSize() . ', but the filesystem reported a size of ' . $fsSize);
 
 				$this->getFileInfo()->getStorage()->getUpdater()->update($this->getFileInfo()->getInternalPath());