Possible negative char to isspace - static analysis warning

[skliper]

Is your feature request related to a problem? Please describe.
In theory a negative value could reach this code through public APIs, which would lead to undefined isspace behavior as it gets converted to int.

cFE/fsw/cfe-core/src/es/cfe_es_syslog.c

Line 432 in 672b2dc

while (StringLen > 0 && isspace((int)Buffer[StringLen-1]))

Describe the solution you'd like
Recommended practice is to cast to unsigned char, such that the conversion to int results in defined behavior.

Describe alternatives you've considered
Could adjust all the parameters involved to unsigned char, but probably not worth it.

Additional context
Static analysis warning

Requester Info
Jacob Hageman - NASA/GSFC

[jphickey]

I went back to the docs on this function, and it says this:

The  c  argument is an int, the value of which the application shall ensure is a character representable as an
unsigned char or equal to the value of the macro EOF. If the argument has any other value, the behavior is un‐
defined.

.... suggests that we actually should cast to unsigned char rather than int when using any of the ctype checks.