[Gmsh] bug: generate counter-clock and clockwise triangle at the same time

[wjian.cd at gmail.com]

gmsh version: 2.8.5 & 2.9.2 windows

global size factor: 0.3

counter-clock and clockwise triangles are generated at the same time. The 
following two triangle are not in the same direction:

13 2 2 3 12 *6 20 23*
14 2 2 3 12 *20 22 23*
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