Resolves cppcheck warnings:

cfgscan.c:475:22: warning: Either the condition 'ch==-1' is redundant or
 isalpha() argument nr 1 can have invalid value. The value is -1 but the
 valid values are '0:255'. [invalidFunctionArg]
    else if (isalpha(ch) || (ch == '_'))
                     ^
cfgscan.c:479:17: note: Assuming that condition 'ch==-1' is not redundant
    else if (ch == EOF)
                ^
cfgscan.c:475:22: note: Invalid argument
    else if (isalpha(ch) || (ch == '_'))
                     ^
cfgscan.c:477:22: warning: Either the condition 'ch==-1' is redundant or
 isdigit() argument nr 1 can have invalid value. The value is -1 but the
 valid values are '0:255'. [invalidFunctionArg]
    else if (isdigit(ch))
                     ^
cfgscan.c:479:17: note: Assuming that condition 'ch==-1' is not redundant
    else if (ch == EOF)
                ^
cfgscan.c:477:22: note: Invalid argument
    else if (isdigit(ch))
                     ^

Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>