Fix bug where default image type argument didn't work for libpannellum.
Fix bug where default image type argument didn't work for libpannellum.

mpetroff/pannellum,mpetroff/pannellum,mpetroff/pannellum,psteph801/psteph801.github.io,psteph801/psteph801.github.io,psteph801/psteph801.github.io,psteph801/psteph801.github.io,mpetroff/pannellum