protected final int startPos(final int n) {
        return n > 0 ? fapos[n - 1] & 0x7fffffff : 0;
    }
Set the internal reader (aboffset, aboffsetEnd) to the body data for the given id
<p>
If a node is not found in an empty cache, this is usually an edge-effect
(data-file does not exist or neighboured data-files of differnt age),
but is can as well be a symptom of a node-identity breaking bug.
<p>
Current implementation always returns false for not-found, however, for
regression testing, at least for the case that is most likely a bug
(node found but marked as deleted = ready for garbage collection
= already consumed) the RunException should be re-enabled

@return true if id was found
main/src/main/java/cgeo/geocaching/brouter/codec/MicroCache.java