Merge branch 'jk/read-in-full'

Code clean-up to prevent future mistakes by copying and pasting code that checks the result of read_in_full() function. * jk/read-in-full: worktree: check the result of read_in_full() worktree: use xsize_t to access file size distinguish error versus short read from read_in_full() avoid looking at errno for short read_in_full() returns prefer "!=" when checking read_in_full() result notes-merge: drop dead zero-write code files-backend: prefer "0" for write_in_full() error check