Improve stability, returns -1 for sequenceId when failed to fetch from server

mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/message/outgoingSourceImpl.kt

@@ -128,8 +128,8 @@ internal class MessageSourceToGroupImpl(
     @OptIn(ExperimentalCoroutinesApi::class)
     override val sequenceId: Int
         get() = when {
-            sequenceIdDeferred.isCompleted -> sequenceIdDeferred.getCompleted() ?: 0
-            !sequenceIdDeferred.isActive -> 0
+            sequenceIdDeferred.isCompleted -> sequenceIdDeferred.getCompleted() ?: -1
+            !sequenceIdDeferred.isActive -> -1
             else -> error("sequenceId not yet available")
         }
 

mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/MessageSource.kt

@@ -76,7 +76,7 @@ sealed class MessageSource : Message, MessageMetadata, ConstrainSingle<MessageSo
     abstract val bot: Bot
 
     /**
-     * 消息 id (序列号).
+     * 消息 id (序列号). 在获取失败时 (概率很低) 为 `-1`.
      **
      * #### 值域
      * 值的范围约为 [UShort] 的范围.