The code that makes this VOP_BMAP call tries to perform a read-ahead I/O
operation. Failing to do that for any reason isn't fatal for `cluster_read()`,
because we still can return some data to the caller. This is consistent with
other places within `cluster_read()`, where error returned by VOP_BMAP is not
returned to the caller - see the `if (nblks > 1)` block above the changed lines
and `if (reqbp)` at the end of the function.
PR: 264196