Only disable zip64 if the size is known

Else we might run into the issue that for an external storage where the
size is not known yet we do not use zip64. Which then of course fails on
large zip files.

Signed-off-by: Roeland Jago Douma <roeland@famdouma.nl>

lib/private/Streamer.php

@@ -76,8 +76,12 @@ class Streamer {
 		 * would still be possible to create an invalid zip32 file (for example,
 		 * a zip file from files smaller than 4GB with a central directory
 		 * larger than 4GiB), but it should not happen in the real world.
+		 *
+		 * We also have to check for a size above 0. As negative sizes could be
+		 * from not fully scanned external storages. And then things fall apart
+		 * if somebody tries to package to much.
 		 */
-		if ($size < 4 * 1000 * 1000 * 1000 && $numberOfFiles < 65536) {
+		if ($size > 0 && $size < 4 * 1000 * 1000 * 1000 && $numberOfFiles < 65536) {
 			$this->streamerInstance = new ZipStreamer(['zip64' => false]);
 		} elseif ($request->isUserAgent($this->preferTarFor)) {
 			$this->streamerInstance = new TarStreamer();