Fixed roll command crashes

[TBTerra]

fixed roll command from crashes when silly user input was given

fixed crashes when:

• dice with 0 sides are rolled
• dice with ? sides are rolled (number of sides not specified)
• dice sets where keeping the highest/lowest ? dice (h or l modifier used but no number provided)
• dice where re-rolling below ? (r modifier used but no number provided)

most of these were due to a bug in the regex where it expected a number of length 0 or more, when it should have expected one of length 1 or more