check arrays are not null and greater than 0

don't need to check if they're the same length as vertices array as
Unity gives an error if they aren't

Author: vkovec

Assets/FbxExporters/Editor/FbxExporter.cs

@@ -1512,19 +1512,19 @@ public MeshInfo (Mesh mesh, Material[] materials)
                 }
 
                 public bool HasValidNormals(){
-                    return Normals != null && Normals.Length >= Vertices.Length;
+                    return Normals != null && Normals.Length >= 0;
                 }
 
                 public bool HasValidBinormals(){
                     return HasValidNormals () && HasValidTangents () && Binormals != null;
                 }
 
                 public bool HasValidTangents(){
-                    return Tangents != null && Tangents.Length >= Vertices.Length;
+                    return Tangents != null && Tangents.Length >= 0;
                 }
 
                 public bool HasValidVertexColors(){
-                    return VertexColors != null && VertexColors.Length >= Vertices.Length;
+                    return VertexColors != null && VertexColors.Length >= 0;
                 }
             }