Fixed FMLRelaunchLog's Newline Handling

`System.out.println("\n")` causes `currentMessage` to start with a newline character, which means `idx` will always be 0 from then on. Therefore if `idx` is 0 messages must still be logged, otherwise no more messages sent to stdout will be logged and they will just accumulate in `currentMessage`. This is a real issue because the first thing that is logged when the sound manager is set up is a newline, and so currently no messages logged by mods are displayed.

Commit which introduced this bug: https://github.com/MinecraftForge/FML/commit/5cc90f060caace93c0bf041d3cc37208f425f623