RFR: 8072128: Fixed missing "++" in _mutex_array[] initialization.

[Max Ockner]

Hello,
Please review this small fix.

Bug ID: 8072128
Webrev: http://cr.openjdk.java.net/~mockner/8072128/
Summary:  The fix for bug 8047290 introduced a bug in mutexLocker.cpp in 
which the index into _mutex_array[] never increments. The bug did not 
cause any test failures, and was caught upon inspection of an hs_err 
file which claimed that no locks were owned.  The solution was to 
restore the original code which increments the index.

Tests: jtreg runtime/Safepoint and runtime/RedefineTests.
To make sure the desired functionality was restored, the change was 
manually tested by crashing the vm during VM_RedefineClasses::doit() 
when we know that some locks are owned, and inspecting the hs_err file. 
This is difficult to write a test for, so it was only done manually.

Thanks,
Max