Check if string empty before substringing

[goreacraft]

Hello,

I think there is a problem in MessageMeddler.java at line 20 as it does not check if a string is emtiefirst and crashes client each time it recieves one.
(Empty strings are be used on servers to format the chat and sent nice things for players to read)

Thank you,

[13:19:17] [Client thread/FATAL]: Unreported exception thrown!
java.lang.StringIndexOutOfBoundsException: String index out of range: -2
at java.lang.String.substring(Unknown Source) ~[?:1.8.0_91]
at vazkii.chatflow.MessageMeddler.onMessageReceived(MessageMeddler.java:20) ~[MessageMeddler.class:?]
at cpw.mods.fml.common.eventhandler.ASMEventHandler_178_MessageMeddler_onMessageReceived_ClientChatReceivedEvent.invoke(.dynamic) ~[?:?]
at cpw.mods.fml.common.eventhandler.ASMEventHandler.invoke(ASMEventHandler.java:54) ~[ASMEventHandler.class:?]
at cpw.mods.fml.common.eventhandler.EventBus.post(EventBus.java:140) ~[EventBus.class:?]
at net.minecraft.client.network.NetHandlerPlayClient.func_147251_a(NetHandlerPlayClient.java:694) ~[bjb.class:?]
at net.minecraft.network.play.server.S02PacketChat.func_148833_a(SourceFile:38) ~[gj.class:?]
at net.minecraft.network.play.server.S02PacketChat.func_148833_a(SourceFile:9) ~[gj.class:?]
at net.minecraft.network.NetworkManager.func_74428_b(NetworkManager.java:212) ~[ej.class:?]
at net.minecraft.client.multiplayer.PlayerControllerMP.func_78765_e(PlayerControllerMP.java:273) ~[bje.class:?]
at net.minecraft.client.Minecraft.func_71407_l(Minecraft.java:1602) ~[bao.class:?]
at net.minecraft.client.Minecraft.func_71411_J(Minecraft.java:973) ~[bao.class:?]
at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:898) [bao.class:?]
at net.minecraft.client.main.Main.main(SourceFile:148) [Main.class:?]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_91]
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_91]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_91]
at java.lang.reflect.Method.invoke(Unknown Source) ~[?:1.8.0_91]
at net.minecraft.launchwrapper.Launch.launch(Launch.java:135) [launchwrapper-1.12.jar:?]
at net.minecraft.launchwrapper.Launch.main(Launch.java:28) [launchwrapper-1.12.jar:?]