main: check "/dev/tty" on startup

ble.pp

@@ -66,16 +66,17 @@
     "  We recommend using ble.sh with a release version of Bash." >&2 ;;
 esac
 
-if [[ $- != *i* ]]; then
+if ((BASH_SUBSHELL)); then
+  builtin echo "ble.sh: ble.sh cannot be loaded into a subshell." >&2
+  return 1 2>/dev/null || builtin exit 1
+elif [[ $- != *i* ]]; then
   case " ${BASH_SOURCE[*]##*/} " in
   (*' .bashrc '* | *' .bash_profile '* | *' .profile '* | *' bashrc '* | *' profile '*) false ;;
   esac  &&
     builtin echo "ble.sh: This is not an interactive session." >&2 || ((1))
-  return 1 2>/dev/null || exit 1
-fi
-
-if ((BASH_SUBSHELL)); then
-  builtin echo "ble.sh: ble.sh cannot be loaded into a subshell." >&2
+  return 1 2>/dev/null || builtin exit 1
+elif ! [[ -t 0 && -t 1 ]]; then
+  builtin echo "ble.sh: cannot find the correct TTY/PTY in this session." >&2
   return 1 2>/dev/null || builtin exit 1
 fi