Fix the bug that causes not allocating free run with lowest address.
Reintroduce the comment that was removed in f9ff603.
Merge pull request #103 from wqfish/dev

Fix the bug that causes not allocating free run with lowest address.

This fixes a regression due to f9ff60346d7c25ad653ea062e496a5d0864233b2,
which was never incorporated into a release.