Incorrect normalization of Er source at r = 0 and m = ±1 in cylindrical coordinates

[oskooi]

In cylindrical coordinates, $E_r$ is defined at the midpoint of the Yee-grid voxels ($r = 0.5\Delta r$). An $E_r$ point source at $r = 0$ and $m = \pm 1$ requires restriction to $E_r$ grid points at $r = \pm 0.5\Delta r$. There is a bug in the restriction operation for this case which prevents computing quantities such as the extraction efficiency involving the ratio of the Poynting flux (add_flux) to the LDoS (dft_ldos).

Based on the results in #2538 (comment), a simple workaround is to place the $E_r$ point source at $r = 1.5\Delta r$. This ensures restriction does not involve $E_r$ grid points within the $r = 0$ voxels. A source placed anywhere at $r < 1.5\Delta r$ triggers the bug, however. This slight adjustment of the source position incurs a small error which decreases with increasing grid resolution (smaller $\Delta r$).