This function checks to see if a category typed into a category box is present in the category record for that box. If not, it is added. The string passed may consist of multiple categories, separated by ';'.
* Syntax: DB_CheckCategory(DBBLOCK *dblk, RECORDNUM categoryrecord,
char far *CategoryString)
DB_OVERFLOW Category record exceeded 256 characters.
Other error returns are as DB_WriteRecord.