st/mesa: improve the guess_and_alloc_texture() heuristic

If GL_BASE_LEVEL==0 and GL_MAX_LEVEL==0 that's a pretty good hint that
there'll be a single mipmap level in the texture.

Google Earth sets the texture's state this way before the first glTexImage
call.  This saves a bit of texture memory.

src/mesa/state_tracker/st_cb_texture.c

@@ -375,6 +375,8 @@ guess_and_alloc_texture(struct st_context *st,
     */
    if ((stObj->base.Sampler.MinFilter == GL_NEAREST ||
         stObj->base.Sampler.MinFilter == GL_LINEAR ||
+        (stObj->base.BaseLevel == 0 &&
+         stObj->base.MaxLevel == 0) ||
         stImage->base._BaseFormat == GL_DEPTH_COMPONENT ||
         stImage->base._BaseFormat == GL_DEPTH_STENCIL_EXT) &&
        !stObj->base.GenerateMipmap &&