[termdesc] don't enable sixel graphics with 0 color registers

src/lib/termdesc.c

@@ -1362,10 +1362,13 @@ int interrogate_terminfo(tinfo* ti, FILE* out, unsigned utf8,
   }
   build_supported_styles(ti);
   if(ti->pixel_draw == NULL && ti->pixel_draw_late == NULL){
+    // color_registers was only assigned if kitty_graphics were unavailable
+    if(ti->color_registers > 0){
+      setup_sixel_bitmaps(ti, ti->ttyfd, invertsixel);
+    }
     if(kitty_graphics){
       setup_kitty_bitmaps(ti, ti->ttyfd, NCPIXEL_KITTY_STATIC);
     }
-    setup_sixel_bitmaps(ti, ti->ttyfd, invertsixel);
   }
   return 0;
 

src/tests/direct.cpp

@@ -74,7 +74,6 @@ TEST_CASE("Direct") {
     }
   }
 
-  /*
 #ifndef NOTCURSES_USE_MULTIMEDIA
   SUBCASE("VisualDisabled"){
     CHECK(!ncdirect_canopen_images(nc_));
@@ -172,7 +171,6 @@ TEST_CASE("Direct") {
     }
   }
 #endif
-  */
 
   CHECK(0 == ncdirect_stop(nc_));