check for duplicated stack addresses by JimLee168

Based on https://code.google.com/p/jpcsp/source/detail?r=3569

Fix WWE SmackDown! vs. RAW 2006,2007,2008 booting
Fix #6671

2006 Modify log: https://gist.github.com/sum2012/a74a7199dcb3058fa5d8
It looks like it is happening on the sdk versions within that check, although I'm not sure about "numStacks".

hrydgard/pspautotests#154

After fixing the bracing `} else if (...`, I recommend verifying it matches the test above.  If it does, then it should be good.

-[Unknown]