[rmodels] Fixed null pointer dereference in LoadGLTF (#4564)

* [rmodels] Fixed null pointer dereference in LoadGLTF

* [rmodels] Add parenthesis around conditionals in LoadGLTF

src/rmodels.c

@@ -5657,7 +5657,7 @@ static Model LoadGLTF(const char *fileName)
                 }
 
                 // Load primitive indices data (if provided)
-                if (mesh->primitives[p].indices != NULL)
+                if ((mesh->primitives[p].indices != NULL) && (mesh->primitives[p].indices->buffer_view != NULL))
                 {
                     cgltf_accessor *attribute = mesh->primitives[p].indices;