[901] String Crash

If you enter a string into ZQuest and adjust the Y position such that all or part of the string is to be written at a point below the lower limit of the screen (>160 or so, though I don't know the exact number offhand where the write fails), ZC will crash when it tries to write to that position. Not a fatal bug, but it would be handy to have a cap on the entered value for the benefit of us dyslexic users.