Font loading from subdirectories fails for nested .ttf files

[geerzo]

This is related to #206 but addresses the .ttf file. Currently if your font is in a subdirectory it will load the .kttf file from the subdirectory but will always look for the .ttf file in the /assets root folder. This can be reproduced by renaming /assets/roboto.ttf to something else and then running the font_size_tests.rs use case.