termview: fix the composition of some keys
termview: fix the composition of some keys

E.g. <A-]> would have been written <A-bracketright> by taking the key
name. By using the string, we get the expected characters, but it may
happen to be NULL sometimes (META+SHIFT). In these cases, we drop the
input, as it worths nothing anyway.

jeanguyomarch/eovim,jeanguyomarch/eovim,jeanguyomarch/eovim