intel: Don't update window system renderbuffers on TexImage.

While sometimes rendering occurs in the form of blits for TexImage, it
doesn't interact with the window system renderbuffers, so skip it.

src/mesa/drivers/dri/intel/intel_context.c

@@ -409,6 +409,10 @@ intel_update_renderbuffers(__DRIcontext *context, __DRIdrawable *drawable)
    driUpdateFramebufferSize(&intel->ctx, drawable);
 }
 
+/**
+ * intel_prepare_render should be called anywhere that curent read/drawbuffer
+ * state is required.
+ */
 void
 intel_prepare_render(struct intel_context *intel)
 {

src/mesa/drivers/dri/intel/intel_tex_image.c

@@ -240,7 +240,7 @@ try_pbo_upload(struct intel_context *intel,
 
    if (drm_intel_bo_references(intel->batch->buf, dst_buffer))
       intel_flush(&intel->ctx);
-   intel_prepare_render(intel);
+
    {
       dri_bo *src_buffer = intel_bufferobj_buffer(intel, pbo, INTEL_READ);
 
@@ -473,8 +473,6 @@ intelTexImage(GLcontext * ctx,
 					   pixels, unpack, "glTexImage");
    }
 
-   intel_prepare_render(intel);
-
    if (intelImage->mt) {
       if (pixels != NULL) {
 	 /* Flush any queued rendering with the texture before mapping. */