vici: Cancel processor before calling library_deinit()

For non-direct libstrongswan users, the deinitialization segfaults because
of the missing worker thread cancellation.

src/libcharon/plugins/vici/libvici.c

@@ -762,5 +762,6 @@ void vici_init()
 
 void vici_deinit()
 {
+	lib->processor->cancel(lib->processor);
 	library_deinit();
 }