djvulibre: one-line patch fixing osx 10.9 breakage

djvudigital & its helpers were producing corrupt djvu files when compiled with clang
gcc builds still work properly
ghostscript (--with-djvu) still works if compiled with clang

No worries, it happens. Just want to make sure we have the necessary information to follow this up on future releases; we've got a few formulae with patches that no-one can remember why they are applied or where they are from...