Invalid polygon geometry (21) in ... dynamically masked I03 data

[ndevenish]

Following basic steps in https://github.com/graeme-winter/dials_tutorials/blob/aa789717f9718e0feb4e6fdefac34d1626ff4a6c/ccp4-workshop-2023/processing_in_detail.md

Invalid polygon geometry (21): (((662.873, 248.435), (757.38, 514.846), (5189.29, 1722.93), (9138.44, 1340.38), (14996.7, -7329.33), (4010.61, -1825.5), (1420.36, -455.091), (953.579, -187.824), (775.609, -68.2139), (697.261, 3.70432), (693.579, 51.1428), (693.579, 51.1428), (670.799, 55.1785), (662.873, 248.435)))
((14996.7, -7329.33), (2540.26, -1017.89), (1482.59, -467.873), (1100.26, -258.571), (910.767, -145.779), (804.032, -73.4832), (741.675, -21.7997), (707.346, 18.1834), (693.579, 51.1428), (693.579, 51.1428), (690.146, 73.2007), (686.802, 94.6875), (683.543, 115.625), (680.367, 136.034), (677.27, 155.935), (674.249, 175.346), (671.301, 194.284), (668.424, 212.768), (665.616, 230.813), (662.873, 248.435), (6701.19, 1450.32), (4010.61, -1825.5), (1420.36, -455.091), (953.579, -187.824), (775.609, -68.2139), (697.261, 3.70432), (670.799, 55.1785), (682.896, 97.2898), (736.548, 136.445), (853.991, 178.811), (1108.16, 235.964), (1820.98, 351.765), (9138.44, 1340.38), (687.343, 144.669), (727.014, 354.347), (757.38, 514.846), (843.394, 533.622), (926.776, 551.823), (1187.33, 551.823), (1447.89, 551.823), (5189.29, 1722.93))

Coming from:

dxtbx/src/dxtbx/masking/goniometer_shadow_masking.h

Lines 156 to 158 in 31f73a5

	std::cout << "Invalid polygon geometry (" << failure
	<< "): " << boost::geometry::dsv(poly) << std::endl;
	std::cout << boost::geometry::dsv(points) << std::endl;

(21) is

failure_self_intersections: The geometry has invalid self-intersections. (applies to areal geometries only)