ResetMassData asserts and crashes client application

[simonvanbernem]

Box2d triggers the assert b2Assert(m_I > 0.0f); at b2_body.cpp:337 when creating a b2Body with a single fixture with density 1 and the b2PolygonShape with the following 3 vertices (given as hex for exact reproducibility):

x0: 0xc28e8d90 //-71.27
y0: 0x42100000 //36.00
x1: 0xc28eb4be //-71.35
y1: 0x42104e5f //36.07
x2: 0xc28ebf3e //-71.37
y2: 0x42100000 //36.00

These vertices seem to survive the vertex welding done by b2PolygonShape::Set just fine, but probably cause rounding errors in exactly the right way to trigger the assert.