(svn r13626) -Fix (r11871): signals were not updated when player removed signals from nonexistent track sharing bits with existing track
So disallow removing signals from nonexistent track

Makefile*
bin/*
!bin/data/chars.grf
!bin/data/openttdd.grf
!bin/data/openttdw.grf
!bin/data/opntitle.grf
!bin/scenario/README
!bin/scripts*
config.*
objs/*
src/rev.cpp