Pull up following revision(s) (requested by kamil in ticket #899):

lib/libutil/passwd.c: revision 1.53

Prevent underflow buffer read in trim_whitespace() in libutil/passwd.c

If a string is empty or contains only white characters, the algorithm of
removal of white characters at the end of the passed string will read
buffer at index -1 and keep iterating backward.

Detected with MKSANITIZER/ASan when executing passwd(1).

(martin)