Fix double dot range for invalid input

[shmsr]

For double dot range i.e., a..b where a and b are inclusive when ranging from a to b. Therefore every element x in the range must satisfy a <= x && x <= b

Previously, it used to panic because, for a..b, a is considered minimum and b is considered maximum which results in negative size when allocating memory for slice using make. Ref:

file: optimizer/const_range.go

size := max.Value - min.Value + 1
...
...
value := make([]int, size)

So, for invalid inputs where a > b, it panics. Similar problem is there in vm/runtime.go's makeRange function as well.

Changing it in the optimizer and makeRange seems apt to me, but I figured it could be handled in checker/checker.go and cry the error out loud that the expression is not correct, but it didn't feel right.

@antonmedv What do you think? Having an empty slice instead of exiting out with an error seems good, right?

Fixes #163

[johejo]

Could you add tests to fix #163 ?

[shmsr]

@johejo done!

[antonmedv]

I think same way work in python. So I think it make sense.

[shmsr]

I think same way work in python. So I think it make sense.

So, this PR looks good, right? Could be merged?

[antonmedv]

Yes, gonna test it today and merge.