cleanup gcc link time optimization warnings

cleanup gcc link time optimization warnings

coord_cache.c: In function 'mcview_ccache_lookup.constprop':
coord_cache.c:374:31: error: 'nextc' may be used uninitialized in this function [-Werror=maybe-uninitialized]
coord_cache.c:342:16: note: 'nextc' was declared here
boxes.c: In function 'sort_box':
boxes.c:877:5: error: 'sort_names_num' may be used uninitialized in this function [-Werror=maybe-uninitialized]
boxes.c:871:11: note: 'sort_names_num' was declared here
actions_cmd.c: In function 'mcview_callback':
actions_cmd.c:252:42: error: 'byte_val' may be used uninitialized in this function [-Werror=maybe-uninitialized]
actions_cmd.c:223:9: note: 'byte_val' was declared here

Signed-off-by: Andreas Mohr <and@gmx.li>
Signed-off-by: Andrew Borodin <aborodin@vmail.ru>