Harden Bash completion scripts against invalid states

Printing an error message is better than locking the shell up, honestly.

contrib/bash_compl/_rgblink.bash

@@ -151,6 +151,10 @@ _rgblink_completions() {
 			done < <(compgen -A directory -- "${cur_word:$optlen}")
 			compopt -o filenames
 			;;
+		*)
+			echo >&2 "Internal completion error: invalid state \"$state\", please report this bug"
+			return 1
+			;;
 	esac
 }