Add details for errors

mirai-core/src/commonMain/kotlin/net.mamoe.mirai/network/protocol/tim/packet/login/PasswordSubmission.kt

@@ -153,19 +153,21 @@ object SubmitPasswordPacket : PacketFactory<SubmitPasswordPacket.LoginResponse,
 
                 discardExact(60)//00 20 01 60 C5 A1 39 7A 12 8E BC 34 C3 56 70 E3 1A ED 20 67 ED A9 DB 06 C1 70 81 3C 01 69 0D FF 63 DA 00 00 01 03 00 14 00 01 00 10 60 C9 5D A7 45 70 04 7F 21 7D 84 50 5C 66 A5 C6
 
+                val flagFront = readUByte().toUInt()
+                val flagBack = readUByte().toUInt()
                 discardExact(
-                    when (readUByte().toUInt()) {
-                        0x00u -> when (readUByte().toUInt()) {
+                    when (flagFront) {
+                        0x00u -> when (flagBack) {
                             0x33u -> 28
                             else -> null
                         }
-                        0x01u -> when (readUByte().toUInt()) {
+                        0x01u -> when (flagBack) {
                             0x07u -> 0
                             0x10u -> 64
                             else -> null
                         }
                         else -> null
-                    } ?: error("Unknown length flag")
+                    } ?: error("Unknown length flag: " + flagFront.toUByte().toUHexString() + flagBack.toUByte().toUHexString())
                 )
 
                 discardExact(23 + 3)//01 D3 00 01 00 16 00 00 00 01 00 00 00 64 00 00 0D DE 00 09 3A 80 00