Vapors from dropped potion of monster detection can cause panic while levitating.

[elunna]

Easy to reproduce.

1. Levitate
2. Make sure all monsters on level are gone
3. Drop a potion of monster detection

The potion will be used up from breaking and then again by the strange feeling handling. I noticed this was previously fixed for thrown and kicked potions but not potions dropped while levitating. It looks like gt.thrownobj is never set in drop() and it just uses the hitfloor() function to handle how things break and such. Could we maybe set gt.thrownobj before hitfloor is called?