simplify OptionUtil#prefixEndOf

[GungnirLaevatain]

What is the purpose of the change

endKey[i] < 0xff is always true, so could simplify this method

Brief changelog

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[AlbumenJ]

@GungnirLaevatain Hi, thanks for your contribution.

Could you please provide more description about this pr?

Do all entries in endKey will always smaller than 0xff ?

[GungnirLaevatain]

@GungnirLaevatain Hi, thanks for your contribution.

Could you please provide more description about this pr?

Do all entries in endKey will always smaller than 0xff ?

range of byte is -128~127, and 0xff is 255, so 'endKey[i] < 0xff' is always true . @AlbumenJ