Fire sources can ignite candles, lamps, and potions of oil

... on the floor, in monster inventory, and in hero's inventory.

Items in your inventory being ignited produce a message even if you're
blind - you can see the lit-state by viewing inventory anyway, so just
give player the message.

(via xNetHack)

src/uhitm.c

@@ -1790,6 +1790,7 @@ int specialdmg; /* blessed and/or silver bonus against various things */
         }
         /* only potions damage resistant players in destroy_item */
         tmp += destroy_mitem(mdef, POTION_CLASS, AD_FIRE);
+        ignite_items(mdef->minvent);
         break;
     case AD_COLD:
         if (negated) {