Exception when material does not have "_MainTex" property

[Liviuss76]

As stated, when material does not have "_MainTex" property, script will spam in console errors.
Solution is to change:
Line 360
from
if (tDetails.material.mainTexture!=null) GUILayout.Box(tDetails.material.mainTexture, GUILayout.Width(ThumbnailWidth), GUILayout.Height(ThumbnailHeight));
to
if (tDetails.material.HasProperty("_MainTex") && tDetails.material.mainTexture!=null) GUILayout.Box(tDetails.material.mainTexture, GUILayout.Width(ThumbnailWidth), GUILayout.Height(ThumbnailHeight));

Line 564
from
if (tMaterial.mainTexture != null && !dependencies.Contains(tMaterial.mainTexture))
to
if (tMaterial.HasProperty("_MainTex") && tMaterial.mainTexture != null && !dependencies.Contains(tMaterial.mainTexture))