Detect division by zero

[dblN]

There happens division by zero if the setting is inappropriate.

• When creating the layer such as convolution or pooling layer, the shape can be 0.
• When stepsize is not specified, it can be 0.

I added checks for these cases.

[ronghanghu]

I think we should have this, or at least the stepsize check. Note this is against #2053 (but I prefer this one since #2053 will potentially introduce lots of new troubles).

[bhack]

/cc @mtamburrano

[bhack]

@ronghanghu We could always improve that if somebody had given us any review feedbacks by months. This one got a reply only after 5 days. See also BAIDU researcher catch almost ignored at #2623 and related PR at #2569.

[mtamburrano]

hi @ronghanghu,
I'm not sure how this PR is against #2053, where that PR let the computation to continue even when some batch becomes 0-sized (probably due to the use of FilterLayer).
This PR only checks if the blob has size 0 and stop computation in that case, so it doesn't fix the use case when a blob is completely filtered on purpose

[bhack]

/cc @prclibo