isspace() must only used with an unsigned char or EOF argument,
and even then its result can depend on the current locale settings.
While this is not a problem for C/C++ executables which use the default
"C" locale, it becomes a problem when the Tesseract API is called from
languages like Python or Java which don't use the "C" locale.
By calling isasci() before calling isspace() this uncertainty can be
avoided, because any locale will hopefully give identical results for
the basic ASCII character set.
Signed-off-by: Stefan Weil <sw@weilnetz.de>