prevent infinite loop when all the missions are cancelled

lib/gsh.sh

@@ -184,11 +184,22 @@ __gsh_start() {
 
     if [ "$exit_status" -ne 0 ]
     then
+      # the GSH_CANCELLED variable keeps track of consecutive cancelled missions
+      # to prevent looping if all the missions are cancelled.
+      # It is unset on the first non-cancelled mission.
+      if echo "$GSH_CANCELLED" | grep -Eq ":$MISSION_NB(:|$)"
+      then
+        echo "$(gettext "Error: no mission was found!
+Aborting.")" >&2
+        exit 1
+      fi
       color_echo yellow "$(eval_gettext "Error: mission \$MISSION_NB is cancelled because some dependencies are not met.")" >&2
+      GSH_CANCELLED=$GSH_CANCELLED:$MISSION_NB
       __log_action "$MISSION_NB" "CANCEL_DEP_PB"
       __gsh_start "$((MISSION_NB + 1))"
       return
     fi
+    unset GSH_CANCELLED
 
     if ! . mainshell.sh
     then

start.sh

@@ -173,7 +173,7 @@ Do you want to remove it and start a new game? [y/N]') "
   # hide cursor and disable echoing of keystrokes
   tput civis 2>/dev/null
   stty -echo 2>/dev/null
-  trap "tput cnorm 2>/dev/null; stty echo 2>/dev/null; echo" INT TERM
+  trap "tput cnorm 2>/dev/null; stty echo 2>/dev/null; echo" INT TERM EXIT
 
 
   # remove all the game data
@@ -380,7 +380,7 @@ Do you want to remove it and start a new game? [y/N]') "
   if [ "$MISSION_NB" -eq 1 ]
   then
     echo "$(gettext "Error: no mission was found!
-Aborting.")"
+Aborting.")" >&2
     exit 1
   fi
   if [ "$GSH_MODE" = "DEBUG" ]