Don't overflow item refcount on get

Counts as a miss if the refcount is too high. ASCII multigets are the only
time refcounts can be held for so long.

doing a dirty read of refcount. is aligned.

trying to avoid adding an extra refcount branch for all calls of item_get due
to performance. might be able to move it in there after logging refactoring
simplifies some of the branches.
static bool grow_stats_buf(conn *c, size_t needed) {
    size_t nsize = c->stats.size;
    size_t available = nsize - c->stats.offset;
    bool rv = true;

    /* Special case: No buffer -- need to allocate fresh */
    if (c->stats.buffer == NULL) {
        nsize = 1024;
        available = c->stats.size = c->stats.offset = 0;
    }

    while (needed > available) {
        assert(nsize > 0);
        nsize = nsize << 1;
        available = nsize - c->stats.offset;
    }

    if (nsize != c->stats.size) {
        char *ptr = realloc(c->stats.buffer, nsize);
        if (ptr) {
            c->stats.buffer = ptr;
            c->stats.size = nsize;
        } else {
            STATS_LOCK();
            stats.malloc_fails++;
            STATS_UNLOCK();
            rv = false;
        }
    }

    return rv;
}

static bool grow_stats_buf(conn *c, size_t needed) {
    size_t nsize = c->stats.size;
    size_t available = nsize - c->stats.offset;
    bool rv = true;

    /* Special case: No buffer -- need to allocate fresh */
    if (c->stats.buffer == NULL) {
        nsize = 1024;
        available = c->stats.size = c->stats.offset = 0;
    }

    while (needed > available) {
        assert(nsize > 0);
        nsize = nsize << 1;
        available = nsize - c->stats.offset;
    }

    if (nsize != c->stats.size) {
        char *ptr = realloc(c->stats.buffer, nsize);
        if (ptr) {
            c->stats.buffer = ptr;
            c->stats.size = nsize;
        } else {
            STATS_LOCK();
            stats.malloc_fails++;
            STATS_UNLOCK();
            rv = false;
        }
    }

    return rv;
}
