fix import hooks bug that returns false (instead of null) when module not found
fix import hooks bug that returns false (instead of null) when module not found

JohnDenker/brython,olemis/brython,Hasimir/brython,firmlyjin/brython,molebot/brython,amrdraz/brython,olemis/brython,firmlyjin/brython,rubyinhell/brython,jonathanverner/brython,Lh4cKg/brython,jonathanverner/brython,molebot/brython,rubyinhell/brython,firmlyjin/brython,kevinmel2000/brython,kikocorreoso/brython,kevinmel2000/brython,Mozhuowen/brython,brython-dev/brython,amrdraz/brython,Lh4cKg/brython,nvoron23/brython,Lh4cKg/brython,olemis/brython,amrdraz/brython,Isendir/brython,amrdraz/brython,Mozhuowen/brython,kikocorreoso/brython,rubyinhell/brython,Isendir/brython,olemis/brython,brython-dev/brython,molebot/brython,brython-dev/brython,Hasimir/brython,Hasimir/brython,kikocorreoso/brython,jonathanverner/brython,Isendir/brython,JohnDenker/brython,nvoron23/brython,Hasimir/brython,Mozhuowen/brython,jonathanverner/brython,Isendir/brython,firmlyjin/brython,JohnDenker/brython,Lh4cKg/brython,kevinmel2000/brython,JohnDenker/brython,firmlyjin/brython,rubyinhell/brython,Mozhuowen/brython,kevinmel2000/brython,nvoron23/brython,molebot/brython