Check if null before calling thread_detach(), fixed compilation warning
Check if null before calling thread_detach(), fixed compilation warning

git-svn-id: ab66a9de07fa9d47c5829c82992f5279466c775f@2572 63c20433-aa62-49bd-875c-5a186b69a8fb

rbouqueau/gpac_brew_travis,porcelijn/gpac,rbouqueau/gpac,emmanouil/gpac,canatella/gpac,nguyen-viet-thanh-trung/gpac,ARSekkat/gpac,ARSekkat/gpac,psteinb/gpac,rauf/gpac,rbouqueau/gpac_brew_travis,vladimir-kazakov/gpac,emmanouil/gpac,ARSekkat/gpac,DmitrySigaev/gpac,rbouqueau/gpac,vladimir-kazakov/gpac,epam/gpac,rbouqueau/gpac_brew_travis,porcelijn/gpac,canatella/gpac,drakeguan/gpac,aymanelyaagoubi/gpac,nguyen-viet-thanh-trung/gpac,porcelijn/gpac,Bevara/Access-open,rbouqueau/gpac,rbouqueau/gpac,Bevara/Access-open,rbouqueau/gpac_brew_travis,canatella/gpac,rauf/gpac,psteinb/gpac,rbouqueau/gpac,gpac/gpac,ARSekkat/gpac,drakeguan/gpac,canatella/gpac,gpac/gpac,rauf/gpac,rbouqueau/gpac_brew_travis,porcelijn/gpac,DmitrySigaev/gpac,rbouqueau/gpac,drakeguan/gpac,DmitrySigaev/gpac,RodolpheFouquet/gpac,Bevara/Access-open,epam/gpac,rauf/gpac,Bevara/Access-open,nguyen-viet-thanh-trung/gpac,epam/gpac,nguyen-viet-thanh-trung/gpac,gpac/gpac,rbouqueau/gpac_brew_travis,emmanouil/gpac,gpac/gpac,nguyen-viet-thanh-trung/gpac,DmitrySigaev/gpac,rauf/gpac,aymanelyaagoubi/gpac,DmitrySigaev/gpac,vladimir-kazakov/gpac,psteinb/gpac,porcelijn/gpac,canatella/gpac,emmanouil/gpac,epam/gpac,rbouqueau/gpac,porcelijn/gpac,RodolpheFouquet/gpac,drakeguan/gpac,aymanelyaagoubi/gpac,drakeguan/gpac,drakeguan/gpac,Bevara/Access-open,canatella/gpac,epam/gpac,psteinb/gpac,RodolpheFouquet/gpac,DmitrySigaev/gpac,RodolpheFouquet/gpac,psteinb/gpac,nguyen-viet-thanh-trung/gpac,epam/gpac,aymanelyaagoubi/gpac,RodolpheFouquet/gpac,aymanelyaagoubi/gpac,gpac/gpac,Bevara/Access-open,RodolpheFouquet/gpac,canatella/gpac,rauf/gpac,vladimir-kazakov/gpac,vladimir-kazakov/gpac,ARSekkat/gpac,emmanouil/gpac,aymanelyaagoubi/gpac,vladimir-kazakov/gpac,gpac/gpac,gpac/gpac,rbouqueau/gpac,ARSekkat/gpac,emmanouil/gpac,psteinb/gpac,gpac/gpac