mesa: Don't call driver RenderTexture for invalid zoffset

mesa: Don't call driver RenderTexture for invalid zoffset

This fixes the segfault in the 'invalid slice of 3D texture' and
'invalid layer of an array texture' subtests of piglit's fbo-incomplete
test.

The 'invalid layer of an array texture' subtest still fails.

v2: Fix off-by-one comparison error noticed by Chris Forbes.  Also,
1D_ARRAY textures have Depth == 1.  Instead, compare against Height.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org> [v1]
Cc: "9.1 9.2" mesa-stable@lists.freedesktop.org