CVE-2026-23141: btrfs: send: check for inline extents in range_is_hole_in_parent()

In the Linux kernel, the following vulnerability has been resolved:

btrfs: send: check for inline extents in rangeisholeinparent()

Before accessing the diskbytenr field of a file extent item we need to check if we are dealing with an inline extent. This is because for inline extents their data starts at the offset of the diskbytenr field. So accessing the diskbytenr means we are accessing inline data or in case the inline data is less than 8 bytes we can actually cause an invalid memory access if this inline extent item is the first item in the leaf or access metadata from other items.