(mc_search__run_regex): optimization

...for case where there is no MC_SEARCH_CB_INVALID or MC_SEARCH_CB_SKIP
return codes (for search from file manager), so we can copy line
at regex buffer all at once.

Thanks Sergey Naumov <sknaumov@gmail.com> for the original patch.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
(mc_search__cond_struct_new_regex_hex_add): refactoring to get rid of extra memory allocation.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
(mc_search__conditions_free): use g_ptr_array_foreach().

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
(mc_search__cond_struct_new_regex_accum_append): minor optimization.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
(mc_search_regex__process_append_str): minor optimization and cosmetics.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>