vector3: return w1 not zero vector

[xianglunkai]

fix liitle bugs when w1=w2

[IamPete1]

Looks like you will also have to update the test.

ardupilot/libraries/AP_Math/tests/test_3d_lines.cpp

Line 29 in 8fa6432

EXPECT_VECTOR3F_EQ((Vector3f{0.0f, 0.0f, 0.0f}), intersection_null);

[xianglunkai]

Thank you! test have been fixed!

[rishabsingh3003]

Ah, that was a mistake I made. Thanks for fixing it!
Did you mean to include th harmonic notch change as well? Not sure if it belongs to this PR

[xianglunkai]

@rishabsingh3003 Txs,only merge vector3 pr.

[amilcarlucas]

@xianglunkai we can not select what parts to merge. You need to remove the harmonic notch change yourself

[xianglunkai]

@amilcarlucas Txs