Fix crash with forward declarations.
Fix crash with forward declarations.

Thanks to Alok Singhal.
madjar/cython,mcanthony/cython,madjar/cython,mcanthony/cython,fperez/cython,ChristopherHogan/cython,mcanthony/cython,mrGeen/cython,fperez/cython,dahebolangkuan/cython,hickford/cython,hhsprings/cython,acrispin/cython,slonik-az/cython,fperez/cython,JelleZijlstra/cython,slonik-az/cython,c-blake/cython,ABcDexter/cython,hhsprings/cython,dahebolangkuan/cython,ChristopherHogan/cython,slonik-az/cython,fabianrost84/cython,scoder/cython,achernet/cython,mcanthony/cython,madjar/cython,encukou/cython,mrGeen/cython,hhsprings/cython,ABcDexter/cython,encukou/cython,cython/cython,scoder/cython,fabianrost84/cython,andreasvc/cython,roxyboy/cython,da-woods/cython,da-woods/cython,cython/cython,ABcDexter/cython,da-woods/cython,marscher/cython,fabianrost84/cython,hickford/cython,roxyboy/cython,dahebolangkuan/cython,JelleZijlstra/cython,hhsprings/cython,ABcDexter/cython,c-blake/cython,da-woods/cython,marscher/cython,fabianrost84/cython,slonik-az/cython,acrispin/cython,slonik-az/cython,dahebolangkuan/cython,fperez/cython,hickford/cython,andreasvc/cython,hickford/cython,madjar/cython,achernet/cython,madjar/cython,roxyboy/cython,mcanthony/cython,mrGeen/cython,JelleZijlstra/cython,JelleZijlstra/cython,encukou/cython,marscher/cython,fperez/cython,hickford/cython,andreasvc/cython,andreasvc/cython,JelleZijlstra/cython,achernet/cython,c-blake/cython,roxyboy/cython,cython/cython,marscher/cython,hhsprings/cython,acrispin/cython,andreasvc/cython,fabianrost84/cython,achernet/cython,encukou/cython,mrGeen/cython,marscher/cython,c-blake/cython,ChristopherHogan/cython,achernet/cython,roxyboy/cython,c-blake/cython,cython/cython,ABcDexter/cython,mrGeen/cython,acrispin/cython,dahebolangkuan/cython,scoder/cython,acrispin/cython,scoder/cython,encukou/cython