_collModInternal has a cmrNew variable that is used in a writeConflictRetry loop, but initialized before the loop begins. Usage of cmrNew must be very careful not to access memory that can become invalid (freed) after an onRollback call caused by a WriteConflictException. After
SERVER-9306, we try to access cmrNew.idx (the unsafe pointer) before initializing it again in the writeConflictRetry loop. The old code, prior to SERVER-9306, did not make this mistake: the access used to be after initializing the pointer, so the pointer was safe for use at that point.