archive: close archive when stream is closed

Fixes a memory leak: the "archive" input plugin opens the archive, but
never closes it.  This patch moves the responsibility for doing that
to archive_plugin.open_stream().  This is an slight internal API
change, but it is the simplest and least intrusive fix for the memory
leak.

src/archive/iso_plugin.c

@@ -165,6 +165,8 @@ iso_is_close(struct input_stream *is)
 {
 	iso_context *context = (iso_context *) is->data;
 	g_free(context->statbuf);
+
+	iso_close((struct archive_file *)context);
 }