Fix issue with iniSet* functions and root section

Bug introduced in commit 0d9111a5: iniSet* functions would write key/values to the end of the list when the root section (NULL) was specified, rather than the beginning of the list.
The root section always starts at the beginning of the list/file, so I'm not sure why section_start() was doing anything other than returning 0 for the root section. It's possible this now breaks iniSortSections() in some way, so that should be retested with a file with a root section and named sections.

src/xpdev/ini_file.c

@@ -195,7 +195,7 @@ static size_t find_section(str_list_t list, const char* section)
 	size_t	i;
 
 	if(section==ROOT_SECTION)
-		return section_start(list, 0);
+		return 0;
 
 	i=find_section_index(list,section);
 	if(list[i]!=NULL)