Fix negative CompressedTexImage2D tests

Fix negative CompressedTexImage2D tests

Certain tests expect GL_VALID_VAULE for
glCompressedTexImage2D(GL_TEXTURE_2D, -1, 0x8b90, 0, 0, 0, 0, 0).

0x8b90 is a palette format PALETTE4_RGB8 and
the OES_compressed_paletted_texture extension allows
negative values for the level parameter:
    Accepted by the <level> parameter of CompressedTexImage2D
        Zero and negative values.  |level| + 1 determines the number of
        mip levels defined for the paletted texture.

This change fixes the tests in presence of
the OES_compressed_paletted_texture extension.

Components: AOSP
Google bug: 38109626

Affects:
dEQP-GLES2.functional.negative_api.texture.compressedteximage2d_neg_level_tex2d
dEQP-GLES2.functional.negative_api.texture.compressedteximage2d_neg_level_cube

Change-Id: Ia37e3fecaf3547abfb209803378114043c63a243