kernel: iomap: fix out-of-bounds bitmap_set() with zero-length range

A flaw was found in the Linux kernel's iomap subsystem. An unsigned subtraction underflow occurs when ifssetrangedirty or ifssetrangeuptodate are called with a zero-length range. This can lead to an out-of-bounds write via bitmapset, potentially allowing a local attacker to cause memory corruptio...