fix error callbacks not being stored

src/core/structures/module-store.ts

@@ -7,6 +7,7 @@ import { CoreModuleStore } from '../contracts';
  * For interacting with modules, use the ModuleManager instead.
  */
 export class ModuleStore implements CoreModuleStore {
+    onError = new WeakMap<Module, Function>();
     metadata = new WeakMap<Module, CommandMeta>();
     commands = new Map<string, string>();
 }

src/core/structures/services/module-manager.ts

@@ -11,6 +11,13 @@ import { CommandType } from '../enums';
 export class DefaultModuleManager implements ModuleManager {
     constructor(private moduleStore: CoreModuleStore) {}
 
+    getErrorCallback(m: Module): Function | undefined {
+        return this.moduleStore.onError.get(m);
+    }
+    setErrorCallback(m: Module, c: Function): void {
+        this.moduleStore.onError.set(m, c);
+    }
+
     getByNameCommandType<T extends CommandType>(name: string, commandType: T) {
         const id = this.get(Id.create(name, commandType));
         if (!id) {