Fix segfault on invalid command line arguments

If FlightGear terminated before the FDM was instantiated it crashed.

diff --git a/src/FDM/fdm_shell.cxx b/src/FDM/fdm_shell.cxx
index bec319c0981847638912233c0e5ebe963df5d512..a4cfad3098969198a5d60a3e765b8ae4ae27cbd8 100644 (file)
--- a/src/FDM/fdm_shell.cxx
+++ b/src/FDM/fdm_shell.cxx
@@ -98,7 +98,7 @@ void FDMShell::bind()
 
 void FDMShell::unbind()
 {
-  _impl->unbind();
+  if( _impl ) _impl->unbind();
 }
 
 void FDMShell::update(double dt)