In the case of modulo wrapping of nsize * 4, the else if block could be
taken even though EA->alloc is not really greater than nsize * 4.  This
can lead to nalloc becoming smaller than nsize, which will result in the
buffer to be reallocated to be smaller than the desired nsize.

This commit adds a comment describing the cases handled by the
if (nalloc < nsize) block.  One such case is the potential wrap
around of EA->alloc * 2.  Without the comment, it was not clear
that the wrap around is properly handled.