Don't throw in mce.py on fill/replace with an empty box
Don't throw in mce.py on fill/replace with an empty box

mce.py, when called with an empty box (e.g., request entire world to be
changed), would throw an exception, since box is None (and therefore has
no volume parameter).  This would prevent the ligthting steps from
occuring further on.

arruda/pymclevel,ahh2131/mchisel,mcedit/pymclevel,codewarrior0/pymclevel,ahh2131/mchisel,mcedit/pymclevel,arruda/pymclevel,codewarrior0/pymclevel