Fix crash in ril_query_passwd_state() ( LP: 1231995 ).

A missing 'else' statement meant that if 'passwd_state'
was invalid, both CALLBACK_WITH_FAILURE *and* _WITH_SUCCESS
are called, which leads to failure as the "-1" passed to
the SUCCESS callback causes a segfault, as "-1" doesn't
map to valid enum, which is used to set a DBus string
property.