Don't stop reading if fread returns an empty string (#20)

This fixes a premature loop termination on empty string read, which can
happen when reading from network streams, leading to packing truncated
files silently.

By explicitly checking against "false", the loop will terminate only if
fread returns a failure.

src/ZipStreamer.php

@@ -356,7 +356,7 @@ private function streamFileData($stream, $compress, $level) {
       $compStream = DeflateStream::create($level);
     }
 
-    while (!feof($stream) && $data = fread($stream, self::STREAM_CHUNK_SIZE)) {
+    while (!feof($stream) && ($data = fread($stream, self::STREAM_CHUNK_SIZE)) !== false) {
       $dataLength->add(strlen($data));
       hash_update($hashCtx, $data);
       if (COMPR::DEFLATE === $compress) {