SwiftTerm crash patch

[migueldeicaza]

Hello friends,

Today I fixed a bug for a crasher that can at minimum be used to crash SwiftTerm when it reads past a buffer. This at least can lead to a denial of service and an ugly crash (#254)

While auditing the code, I found a few instances that could have also lead to crashes, and I fixed those, you might want to update to the latest commit, or pick this patch

49575ce