pwl.c: fixes for portability
pwl.c: fixes for portability

Testing on MinGW showed that a couple of file modes needed the “b” flag
adding, and that a file positioning operation needed inserting between a
read and a write.

albbas/enchant,albbas/enchant,albbas/enchant,AbiWord/enchant,rrthomas/enchant,rrthomas/enchant,AbiWord/enchant,AbiWord/enchant,albbas/enchant,rrthomas/enchant,rrthomas/enchant,AbiWord/enchant