xray: allow video to show through (blend bg)

src/demo/xray.c

@@ -30,7 +30,7 @@ make_slider(struct notcurses* nc, int dimy, int dimx){
   int r = 0x5f;
   int g = 0xaf;
   int b = 0x84;
-  ncplane_set_bg_alpha(n, CELL_ALPHA_BLEND);
+  ncplane_set_bg_alpha(n, CELL_ALPHA_TRANSPARENT);
   for(int x = 0 ; x < REPS ; ++x){
     for(size_t l = 0 ; l < sizeof(leg) / sizeof(*leg) ; ++l){
       ncplane_set_fg_rgb_clipped(n, r + 0x8 * l, g + 0x8 * l, b + 0x8 * l);

src/lib/render.c

@@ -140,6 +140,8 @@ cellcmp_and_dupfar(egcpool* dampool, cell* damcell,
             return 0; // simple match
           }
         }else{
+          assert(srcplane);
+          assert(srcplane->pool.pool);
           const char* damegc = egcpool_extended_gcluster(dampool, damcell);
           const char* srcegc = extended_gcluster(srcplane, srccell);
           if(strcmp(damegc, srcegc) == 0){