The isspace/isctrl/etc functions require unsigned char as input

Using signed char is documented to be undefined behavior.
2 jobs for release/21.08 in 9 minutes and 56 seconds (queued for 7 seconds)
Status Name Job ID Coverage
  Build
passed build_clazy_clang_tidy #119391

00:09:56

passed reuse #119390
reuse

00:00:23