qrcode: fix ncvisual memory leak

src/demo/zoo.c

@@ -146,6 +146,7 @@ draw_background(struct notcurses* nc){
       return -1;
     }
     ncplane_greyscale(n);
+    ncvisual_destroy(ncv);
   }
   return 0;
 }

src/lib/fill.c

@@ -617,6 +617,7 @@ int ncplane_qrcode(ncplane* n, ncblitter_e blitter, int* ymax,
         }
         ncvisual_geom(n->nc, ncv, &vopts, NULL, NULL, &yscale, &xscale);
       }
+      ncvisual_destroy(ncv);
     }
   }
   free(src);