Fix Service_ModeTranslation memory corruption
In HandleServiceModeTranslation, make sure WsPtr is initialised correctly before trying to use it. Fixes system heap corruption when responding to Service_ModeTranslation (most likely overwriting part of ChocolateMABlocks, and causing a crash when loading future modules)
Fixes issue reported on forums: https://www.riscosopen.org/forum/forums/11/topics/15973