Minor changes to RichTrackSegment::StateErrors constructors

Just for long term consistency, please cherry pick to run2-patches as well.

• [2018-05-11 00:12] Validation started with lhcb-lcg-dev4#521
• [2018-05-11 00:13] Validation started with lhcb-clang-test#948
• [2018-05-11 00:13] Validation started with lhcb-gaudi-head-py3#150
• [2018-05-11 00:14] Validation started with lhcb-lcg-dev3#521
• [2018-05-11 00:14] Validation started with lhcb-gaudi-head#1863
• [2018-05-11 00:15] Validation started with lhcb-head#1849
• [2018-05-11 00:17] Validation started with lhcb-tdr-test#147
• [2018-05-11 02:21] Validation started with lhcb-lcg-dev3#521
• [2018-05-11 02:53] Validation started with lhcb-gaudi-head#1863
• [2018-05-11 05:52] Validation started with lhcb-lcg-dev3#521
• [2018-05-11 08:27] Validation started with lhcb-gaudi-merge#512
• [2018-05-11 11:36] Validation started with lhcb-gaudi-merge#513

merged

mentioned in commit bb42e6d1

mentioned in commit 225b2889

mentioned in merge request !1318 (merged)