Bug correction in look_at

sweet_matrix.c

@@ -245,6 +245,7 @@ sweet_matrix_look_at (vec3 pos, vec3 dir, vec3 up)
     mat4 t;
     vec3 cross;
     cross = sweet_vector_cross (up, dir);
+    cross = sweet_vector_normalize3 (cross);
 
     m.v[0] = cross.x;
     m.v[1] = up.x;