Fix allocation count

The realloc case in continueWrite should not increment the counter,
the pointer passed to realloc is guaranteed to be non-NULL so the total
number of allocations will not have changed.

When realloc is called in restartWrite mData has not been checked
against NULL, increment the counter if it was NULL.

Bug: 26086286
Change-Id: I4c8af450cca1868b91793c0c5f0d8c4b4b5badbe