nir/lower_tex: avoid adding invalid LOD to RECT textures

this is illegal

Fixes: 74ec2b12be ("nir/lower_tex: Rework invalid implicit LOD lowering")

Reviewed-by: Jason Ekstrand <jason.ekstrand@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15804>
(cherry picked from commit 6cfcf891c1)

.pick_status.json

@@ -4036,7 +4036,7 @@
         "description": "nir/lower_tex: avoid adding invalid LOD to RECT textures",
         "nominated": true,
         "nomination_type": 1,
-        "resolution": 0,
+        "resolution": 1,
         "because_sha": "74ec2b12be17a7796186b3100a5a6b208be45b23"
     },
     {

src/compiler/nir/nir_lower_tex.c

@@ -1471,8 +1471,10 @@ nir_lower_tex_block(nir_block *block, nir_builder *b,
       /* Only fragment and compute (in some cases) support implicit
        * derivatives.  Lower those opcodes which use implicit derivatives to
        * use an explicit LOD of 0.
+       * But don't touch RECT samplers because they don't have mips.
        */
       if (nir_tex_instr_has_implicit_derivative(tex) &&
+          tex->sampler_dim != GLSL_SAMPLER_DIM_RECT &&
           !nir_shader_supports_implicit_lod(b->shader)) {
          lower_zero_lod(b, tex);
          progress = true;