Leave a gap between all handles because ringbuf_add_cross interprets equal pointers...

Leave a gap between all handles because ringbuf_add_cross interprets equal pointers as empty, corruption guard check could fail to detect overlap if buffering ran right up to the next handle and it gets asked to buffer again before freeing the following handles (adds a byte on average). Storage alignment on handle reset must at times avoid alignment increments if after a stopped rebuffer, the handle was shrunk too close to the next one or the reading position in a prior rebuffer.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@29302 a1c6a512-1295-4272-9138-f99709370657