mesa: Also handle GL_TEXTURE_EXTENRAL_OES in max num levels.

Reviewed-by: Chad Versace <chad.versace@linux.intel.com>

src/mesa/main/teximage.c

@@ -1056,6 +1056,7 @@ _mesa_get_tex_max_num_levels(GLenum target, GLsizei width, GLsizei height,
       size = MAX3(width, height, depth);
       break;
    case GL_TEXTURE_RECTANGLE:
+   case GL_TEXTURE_EXTERNAL_OES:
       return 1;
    default:
       assert(0);