RFR: 8221836: Avoid recalculating String.hash when zero

[Claes Redestad]

On 2019-04-08 12:15, Andrew Dinn wrote:
> Claes, is there a reason why you named the argument to method
> hash_is_set 'string' when every other method uses the name
> 'java_string'? Is you 'j' key a tad sticky?

I took the cue from set_hash which uses the 'string' naming,
but yes, you're right to point out naming of arguments in
this API is now a bit inconsistent.

/Claes