fix #34; With 'Screen Space - Camera' render mode, sorting is incorrect

UIParticle.cs

@@ -264,6 +264,16 @@ namespace Coffee.UIExtensions
 
 				if (m_ParticleSystem && canvas)
 				{
+					if (canvas.renderMode != RenderMode.ScreenSpaceOverlay)
+					{
+						Vector3 pos = rectTransform.localPosition;
+						if (Mathf.Abs (pos.z) < 0.01f)
+						{
+							pos.z = 0.01f;
+							rectTransform.localPosition = pos;
+						}
+					}
+
 					var rootCanvas = canvas.rootCanvas;
 					Profiler.BeginSample ("Disable ParticleSystemRenderer");
 					if (Application.isPlaying)