Fix parse error in debug version when undefining a float variable.
Fix parse error in debug version when undefining a float variable.

See <web.5f351a7de6b33f6a4d00143e0@news.povray.org>

POV-Ray/povray,c-lipka/povray,POV-Ray/povray,POV-Ray/povray,c-lipka/povray,c-lipka/povray,POV-Ray/povray,POV-Ray/povray,POV-Ray/povray,c-lipka/povray,POV-Ray/povray