Resolve a few more const issues within metadata.c
Resolve a few more const issues within metadata.c

liblouis/liblouis,liblouis/liblouis,BueVest/liblouis,BueVest/liblouis,hammera/liblouis,hammera/liblouis,liblouis/liblouis,BueVest/liblouis,liblouis/liblouis,hammera/liblouis,BueVest/liblouis,BueVest/liblouis,hammera/liblouis,liblouis/liblouis,liblouis/liblouis,hammera/liblouis,BueVest/liblouis,hammera/liblouis