questionable code in fileOperation and distributedTriSurfaceMesh

@andy @Mattijs
by inspection, the following look suspicious:

In masterUncollatedFileOperation::read() the return value (ok) will always be true for global objects since the second declaration of bool ok = false masks the value of the outer bool ok. Needs modification or at least a comment if this is the intended behaviour.

In distributedTriSurfaceMesh::findLocalInstance() it has this type of code:

// Modified findInstance which also looks in parent directory
word instance
(
    io.time().findInstance
    (
        io.local(),
        word::null,
        IOobject::READ_IF_PRESENT
    )
);

if (instance.size())
{
    return instance;
}

but since Time::findInstance returns "constant" if the READ_IF_PRESENT does not find a time instance the remaining code is never seen at all.