Fixed texture sample project broken by prior commit.
Fixed texture sample project broken by prior commit.

It would complain that mipmaps are requested on a texture that
already has mipmaps built-in. Now it simply allows this.

Change-Id: I345403173d957b70fec1192705d57b4997f3c1a6
Tested: on Linux.

google/fplbase,google/fplbase,google/fplbase,google/fplbase