Fix scheduler bug where it rounds to 0 divisions for a chunk.

[DrTodd13]

Resolves #6749

[stuartarchibald]

Manually testing against the sample code in #6749... mainline does this:

num_dim = 6
ranges = ([0, 1], [0, 1], [0, 1], [0, 1], [0, 1], [0, 14], )
num_threads = 4
sched[0] = 1 0 1 0 1 0 1 0 -787390336 271947308 -463249520 271765979 
sched[1] = -769903936 -167047680 307827184 -463126000 0 316800560 -332696768 -787390336 317704688 272245250 0 317704688 
sched[2] = 0 0 -332320592 -770377632 -787390336 316800560 307827184 318603472 -787390336 272247143 -787390336 -463126000 
sched[3] = -770377632 318604000 -812855408 272305680 307819792 315285840 307819864 318603832 0 271783384 32 1241058768 

this patch does:

num_dim = 6
ranges = ([0, 1], [0, 1], [0, 1], [0, 1], [0, 1], [0, 14], )
num_threads = 4
sched[0] = 0 0 0 0 0 0 1 1 1 1 0 6
sched[1] = 0 0 0 0 1 0 1 1 1 1 1 6
sched[2] = 0 0 0 0 0 7 1 1 1 1 0 14
sched[3] = 0 0 0 0 1 7 1 1 1 1 1 14

which I think confirms it fixes the issue.

[stuartarchibald]

Thanks for the patch!