Added log when av_dict fails (cf #59)
Added log when av_dict fails (cf #59)

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