Seed catalog records discarded levels

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When a level fails to generate, it is discarded and a new level is dug from scratch, but the seed catalog records items placed due to reward rooms and key holders from the discarded level.

The placeStairs() call here fails, causing digDungeon() to be called again, but the floorItems remain: https://github.com/tmewett/BrogueCE/blob/af0d25995221a51591ae7da4ba95c2fd28b1acc0/src/brogue/RogueMain.c#L699

Noticed by nstoddard on Discord: https://discord.com/channels/205277826788622337/205347357745872896/1441935621101715599 https://discord.com/channels/205277826788622337/205347357745872896/1441958895248736309

Seed 893623 - Depth 10

These items are seen by the player: CE 1.11,893623,10,1,scroll,remove curse,,,,,,, CE 1.11,893623,10,1,weapon,spear,-1,,,,,, CE 1.11,893623,10,1,potion,life,,,,,,,

These items were generated by a previous attempt to dig the level: CE 1.11,893623,10,1,key,door key,,,,-1,,, CE 1.11,893623,10,1,scroll,enchanting,,,,,,, CE 1.11,893623,10,1,key,door key,,,,-1,,, CE 1.11,893623,10,1,potion,paralysis,,,,,,, CE 1.11,893623,10,1,potion,caustic gas,,,,,,, CE 1.11,893623,10,1,potion,incineration,,,,,,, CE 1.11,893623,10,1,potion,confusion,,,,,,, CE 1.11,893623,10,1,potion,telepathy,,,,,,, CE 1.11,893623,10,1,key,cage key,,,,,,, CE 1.11,893623,10,1,key,cage key,,,,,,, CE 1.11,893623,10,1,staff,conjuration,3,,,,,, CE 1.11,893623,10,1,ring,regeneration,2,,,,,, CE 1.11,893623,10,1,staff,lightning,3,,,,,, CE 1.11,893623,10,1,weapon,dagger,0,,,,,, CE 1.11,893623,10,1,weapon,axe,0,,,,,, CE 1.11,893623,10,1,weapon,war pike,1,,,,,, CE 1.11,893623,10,1,wand,beckoning,4,,,,,, CE 1.11,893623,10,1109,gold,gold pieces (6 piles),,,,,,, CE 1.11,893623,10,1,key,door key,,,,-1,vampire,, CE 1.11,893623,10,1,ally,dar blademaster,,,,,,shackled, CE 1.11,893623,10,1,ally,dar blademaster,,,,,,shackled, CE 1.11,893623,10,1,ally,salamander,,,,,,shackled,