Add some casts for gcc 4.8.3 with more-than-default warnings enabled.
diff --git a/lib/zip.h b/lib/zip.h
index 3b51208..88a44a4 100644
--- a/lib/zip.h
+++ b/lib/zip.h
@@ -236,6 +236,7 @@
     zip_int64_t offset;
     int whence;
 };
+
 typedef struct zip_source_args_seek zip_source_args_seek_t;
 #define ZIP_SOURCE_GET_ARGS(type, data, len, error) ((len) < sizeof(type) ? zip_error_set((error), ZIP_ER_INVAL, 0), NULL : (type *)(data))