SharpClaw reconstruction doesn't provide values in all ghost cells

[ketch]

The high-order WENO routines in SharpClaw don't bother to reconstruct in all ghost cells, because the full algorithm doesn't require reconstructed values there. Riemann problems only need to be solved at interfaces that lie within the (closed) physical domain. However, in the Classic algorithm one needs to solve Riemann problems at certain ghost interfaces in order to have the waves needed for the limiter. So the Riemann solvers are written to loop over those ghost interfaces.

This means that with SharpClaw, some Riemann solves are done at ghost interfaces where the inputs (ql, qr) are uninitialized. This usually doesn't cause problems since we don't ever use the output from those Riemann problems. But, for instance, if one is checking the physical correctness of values within the Riemann solver, this can cause problems.