r300g: cleanup clip state emission

src/gallium/drivers/r300/r300_state.c

     clip->clip = *state;
 
     if (r300->screen->caps.has_tcl) {
-        BEGIN_CB(clip->cb, 29);
-        OUT_CB_REG(R300_VAP_PVS_VECTOR_INDX_REG,
-                (r300->screen->caps.is_r500 ?
-                 R500_PVS_UCP_START : R300_PVS_UCP_START));
-        OUT_CB_ONE_REG(R300_VAP_PVS_UPLOAD_DATA, 6 * 4);
-        OUT_CB_TABLE(state->ucp, 6 * 4);
+        r300->clip_state.size = 2 + !!state->nr * 3 + state->nr * 4;
+
+        BEGIN_CB(clip->cb, r300->clip_state.size);
+        if (state->nr) {
+           OUT_CB_REG(R300_VAP_PVS_VECTOR_INDX_REG,
+                   (r300->screen->caps.is_r500 ?
+                    R500_PVS_UCP_START : R300_PVS_UCP_START));
+           OUT_CB_ONE_REG(R300_VAP_PVS_UPLOAD_DATA, state->nr * 4);
+           OUT_CB_TABLE(state->ucp, state->nr * 4);
+        }
         OUT_CB_REG(R300_VAP_CLIP_CNTL, ((1 << state->nr) - 1) |
                 R300_PS_UCP_MODE_CLIP_AS_TRIFAN);
         END_CB;