Fix rare case of UDP download failing to decompress.

If inflate() produces exactly sizeof(buffer) output, progress may not be
possible if all input has been consumed. As per zlib usage example,
Z_BUF_ERROR must be ignored in this case.

src/client/download.c

@@ -329,7 +329,7 @@ static bool inflate_udp_download(byte *data, int size, int decompressed_size)
         z->avail_out = sizeof(buffer);
 
         ret = inflate(z, Z_SYNC_FLUSH);
-        if (ret != Z_OK && ret != Z_STREAM_END) {
+        if (ret != Z_OK && ret != Z_STREAM_END && ret != Z_BUF_ERROR) {
             Com_EPrintf("[UDP] Error %d decompressing download\n", ret);
             finish_udp_download(NULL);
             return false;