RFR: Optimize oop/fwdptr/hr_index verification a bit

[Roman Kennke]

Am 05.12.2017 um 16:35 schrieb Aleksey Shipilev:
> http://cr.openjdk.java.net/~shade/shenandoah/verifier-perf-hr/webrev.01/
> 
> This slightly optimizes verification code, which should make fastdebug builds run a bit faster.
> 
> Testing: hotspot_gc_shenandoah
> 
> Thanks,
> -Aleksey
> 

Tried it out. Seems to work. Please push!

Roman