Fix erlfdb_database_set_option `else` case

[nickva]

This was detected with more a recent compiler as an uninitialized variable:

c_src/main.c: In function 'erlfdb_database_set_option':
c_src/main.c:818:9: error: 'option' may be used uninitialized in this function [-Werror=maybe-uninitialized]