PASCOMPL: Register usage bug in write(...)

[leobru]

Computing a variable range set uses I12 which contains the file pointer for the I/O routines but write(...) processing overwrites the register usage map and doesn't restore the file pointer to I12 after computing the expression.
Therefore, writeln('some string', value IN [low..high]); skips the Boolean or crashes.
A fix should maintain the existing optimization of write(a, b, c, d); not setting I12 before each item because the write routines themselves do not corrupt the file pointer.