[forEach-of] Guarding against starting index + negative step size
[forEach-of] Guarding against starting index + negative step size

- Example: 'forEach (i of collection from i1 step -1)'
- Does not draw any information from 'collection'
- Better equivalent: 'forEach (i in i1 downTo 0)'
- Old version generated warnings in C.

AbePralle/Rogue,AbePralle/Rogue