fix(extension): 修复创建扩展对象时可能会出现的 NPE 问题.

创建对象后没有检查 NPE 问题, 修复该问题后有助于接受 Factory 不提供扩展的情况(现在这个情况是允许的了).

scalabot-app/src/main/kotlin/ExtensionComponents.kt

@@ -90,6 +90,10 @@ internal class ExtensionLoader(
             try {
                 val extension =
                     factory.createExtensionInstance(bot, getExtensionDataFolder(extensionArtifact))
+                if (extension == null) {
+                    log.debug { "Factory ${factory::class.java} 创建插件时返回了 null, 已跳过. (BotName: ${bot.botUsername})" }
+                    continue
+                }
                 factories.add(LoadedExtensionEntry(extensionArtifact, factory::class.java, extension))
             } catch (e: Exception) {
                 log.error(e) { "创建扩展时发生异常. (ExtArtifact: `$extensionArtifact`, Factory: ${factory::class.java.name})" }