Steps to reproduce:
1. Open user attached project (ParticleSharedMaterialsBug)
2. Open ParticleMaterialsTest.unity scene
3. Play the scene
4. Notice that an additional sharedMaterial is returned in console

Expected result: ParticleSystem.sharedMaterials should not return an additional null material
Actual result: ParticleSystem.sharedMaterials returns an additional null material

Reproduced in: 2017.2.0b3, 2017.1.0f3, 5.6.2p3, 5.5.4p2, 5.5.0a6
Not reproduced in: 5.4.5p4, 5.3.8f2
Regression since: 5.5.0a6