Fix context not freed when replacing error handlers and import resolvers

src/cowl_config.c

@@ -82,6 +82,7 @@ CowlErrorHandler cowl_get_error_handler(void) {
 }
 
 void cowl_set_error_handler(CowlErrorHandler handler) {
+    if (global_error_handler.free) global_error_handler.free(global_error_handler.ctx);
     global_error_handler = handler;
 }
 

src/cowl_manager.c

@@ -215,11 +215,13 @@ void cowl_manager_set_writer(CowlManager *manager, CowlWriter writer) {
 }
 
 void cowl_manager_set_import_resolver(CowlManager *manager, CowlImportResolver resolver) {
+    if (manager->resolver.free) manager->resolver.free(manager->resolver.ctx);
     if (!resolver.resolve_import) resolver = cowl_import_resolver_default(manager);
     manager->resolver = resolver;
 }
 
 void cowl_manager_set_error_handler(CowlManager *manager, CowlErrorHandler handler) {
+    if (manager->handler.free) manager->handler.free(manager->handler.ctx);
     manager->handler = handler;
 }