hkl peak list generation fails in some cases

[jonwright]

For this trigonal cell (calcite) there is a bug in unitcell.py:

uc = ImageD11.unitcell.unitcell([ 6.36,6.36,6.36,46.1,46.1,46.1], 'P')
uc.makerings(0.4)
for d, hl in uc.ringhkls.items():
    print("M=",len(hl),str(hl),d)

The last 3 peaks are not the right multiplicity, I guess the hkl loops were cut short early:

M= 2 [(-1, -1, -1), (1, 1, 1)] 0.176276802603041
M= 6 [(-1, 0, 0), (0, -1, 0), (0, 0, -1), (0, 0, 1), (0, 1, 0), (1, 0, 0)] 0.23918270263279137
M= 6 [(-1, -1, 0), (-1, 0, -1), (0, -1, -1), (0, 1, 1), (1, 0, 1), (1, 1, 0)] 0.2599349962664579
M= 4 [(-2, -1, -1), (-1, -2, -1), (-1, -1, -2), (1, 1, 2)] 0.33014777065022277
M= 1 [(-2, -2, -2)] 0.352553605206082
M= 3 [(-2, -2, -1), (-1, -2, -2), (-2, -1, -2)] 0.37426068668945656