Add a blank string sanity check to corrections.py

This prevents... hanky panky:

> \<neersighted> welcome to mcdona's
> \<Aiden880> s//                      /
> \<Hylin> Correction, \<neersighted>                       w                      e                      l                      c                      o                      m                      e                                             t                      o                                             m                      c                      d                      o                      n                      a