Always panic if len of varlena exceeds the maximum

[YohDeadfall]

The documentation is fixed due to being incorrect, 4294967295 >> 2 is division by 4. And the reason of panicking is that it's promised too.

[workingjubilee]

@YohDeadfall There is a more memorable number that is the limit.

1 gigabyte (specifically, 1024 1024 1024).