FlightGear unterminated index fix (OLDER)

For version 2.10.0.3. The error:

Nasal runtime error: unterminated index (looking for ']')
  at C:/Program Files/FlightGear 2.10.0.3/data/Aircraft/777/Nasal/systems.nas, line 238
  called from: C:/Program Files/FlightGear 2.10.0.3/data/Aircraft/777/Nasal/systems.nas, line 56
  called from: C:/Program Files/FlightGear 2.10.0.3/data/Nasal/globals.nas, line 100

Option 1 - The Fix, "inline":

    update_nd_plan_center : func {
        # find wpt lat, lon
		var index = me.nd_plan_wpt.getValue();
		if (num(index) == nil) return; # Kwynn added this line -  This was originally line 237, error was on 238

Option 2 - replacement for systems.nas

Discussion

I only see this occasionally, but I saw it immediately when I tested v0.8.0 of my script. I can't conceive of the fix doing unintended harm, but I haven't flown much since I made the change.

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