mesa/srgb: handle SARGB8 case in the sw fbo renderer.

src/mesa/main/texrender.c

@@ -595,6 +595,10 @@ update_wrapper(struct gl_context *ctx, const struct gl_renderbuffer_attachment *
       trb->Base.DataType = CHAN_TYPE;
       trb->Base._BaseFormat = GL_RGBA;
       break;
+   case MESA_FORMAT_SARGB8:
+      trb->Fetchf = _mesa_get_texel_fetch_func(MESA_FORMAT_ARGB8888, _mesa_get_texture_dimensions(att->Texture->Target));
+      trb->Base.DataType = CHAN_TYPE;
+      trb->Base._BaseFormat = GL_RGBA;
    default:
       trb->Base.DataType = CHAN_TYPE;
       trb->Base._BaseFormat = GL_RGBA;