maint: regularize struct initializers

maint: regularize struct initializers

* src/chmod.c (process_file):
* src/df.c (replace_invalid_chars):
* src/iopoll.c (iopoll_internal):
* src/ls.c (quote_name_buf):
* src/pathchk.c (portable_chars_only):
* src/printf.c (STRTOX):
* src/shred.c (main):
* src/stat.c (neg_to_zero, do_stat):
* src/timeout.c (settimeout):
* src/tr.c (card_of_complement):
* src/wc.c (wc):
Prefer ‘{0}’ to initialize everything to zero.
* src/stat.c (do_stat):
* src/timeout.c (settimeout):
Do not assume the usual order for struct members,
as POSIX does not guarantee this.