Overflow in size hints in bundles

Consider following program:

```haskell
import qualified Data.Vector.Unboxed as U

main :: IO ()
main = do
print $ U.take 4 $ U.generate (maxBound - 4) id
U.++ U.generate (maxBound - 4) id
```

One could think that it will print `[0,1,2,3]` provided it will fuse. It however fails with.

```
overflow: Data.Vector.Fusion.Bundle.Size.checkedAdd: overflow: -10
CallStack (from HasCallStack):
error, called at src/Data/Vector/Fusion/Bundle/Size.hs:56:7 in vector-0.13.0.1-KtkGVThkqZeLj5OVQdyUBP:Data.Vector.Fusion.Bundle.Size
```

This happens because computation of both exact vector length and upper bound on vector size throws error if it overflows `Int`. I wasn't able to craft example which overflows maximum bound on length which is much more realistic.

This issue is mostly to record that error on error on overflow could cause problems. I'd propose following semantics change: overflow for upper bound on vector size reverts to unbounded. Overflow for lower bound does cause error. (Note not expressible with current implementation of size)

Related: #388