Scan every toroidal plane for the axis guess of a lasym run

[CharlesCNorton]

Fixes #21.

guess_axis already computes the number of planes it has to scan,

if (.not.lasym) then
  ivmax = nzeta/2+1
else
  ivmax = nzeta
end if

but the plane loop runs to nzeta/2+1 regardless, so for lasym = T the entries rcom(nzeta/2+2:nzeta) and zcom(nzeta/2+2:nzeta) reach the axis Fourier transform unassigned. The loop now uses ivmax, which is the same bound as before for lasym = F and covers the whole toroidal range otherwise. PARVMEC guess_axis.f:132 scans all nzeta planes for the same reason.

Checked with input.cma run with LASYM = F and LASYM = T, the latter with every asymmetric coefficient left at zero. Both trigger the axis reguess. Before this change the asymmetric run stops with The jacobian was non-definite! at ns = 25; after it, both runs terminate normally at ns = 51 and their wout files agree to the 1e-6 force tolerance of the case. wout_cma.nc, wout_solovev.nc and wout_cth_like_fixed_bdy.nc are unchanged bit for bit, since ivmax is nzeta/2+1 in the symmetric branch.

VMEC++ carries the same half-range loop at guess_magnetic_axis.cc:382, fixed in proximafusion/vmecpp#787.