fix more MSVC warnings
diff --git a/cs.c b/cs.c
index 2095280..9cc98a3 100644
--- a/cs.c
+++ b/cs.c
@@ -517,7 +517,7 @@
 
 			if (handle->skipdata_setup.callback) {
 				skipdata_bytes = handle->skipdata_setup.callback(buffer_org, size_org,
-						offset - offset_org, handle->skipdata_setup.user_data);
+						(size_t)(offset - offset_org), handle->skipdata_setup.user_data);
 				if (skipdata_bytes > size)
 					// remaining data is not enough
 					break;