Raise the image line/area limits to 8k
Increase the max next slot to process lines to > 8k. Increase the max work area for internal images to allow 8k x 8k. Given a choice of creating a large dynamic area or using the app slot, prefer the latter. Fix bug reusing a stale area address when trying to process an image > max work area:
- ChangeFSI switches to buffer via file mode
- On completion of processing the buffer is freed, but the area address returned anyway
- Desktop front end tries to read the sprite name from the (now absent) area, leading to an abort in ReturnName in the kernel's sprite handler this would complete correctly if done via the command line.
Tested with a 7200x5400 PNG. Now loads correctly on a large memory machine, and reports "Can't get enough memory to process image" on a 64MB Risc PC. Fixes https://www.riscosopen.org/forum/forums/1/topics/3977?page=5#posts-125179