If we pass in a position or velocity of nan, openal will generate an assertion. Under rare circumstances we could encounter a non-cooperative external fdm that could trigger this condition.  This patch catches the problem and returns rather than letting FG get killed.
If we pass in a position or velocity of nan, openal will generate an assertion.
Under rare circumstances we could encounter a non-cooperative external fdm
that could trigger this condition.  This patch catches the problem and returns
rather than letting FG get killed.

slowriot/simgear,slowriot/simgear