Fix items spawned with too much damage

Killing blobs results in " blob glob" (with a space in front).
This space comes from item.cpp:944 - the damage value of the blob item is above 4 and the material class has no damage adjective for this and returns an empty string.

The glob is created with a damage value of rng(5,10) in mondeath.cpp and `map::spawn_an_item` did not correctly clip that value.

The PR corrects the check in `map::spawn_an_item` and also uses rng(1,4) for the damage of the new item (otherwise the damage would always be clipped to 4 anyway).

The same issue appears with rags from a hulk.