patch [#34103]

from Lawrence D'Oliveiro (ldo)

More use of bool type, necessitating adding inclusion of BLI_utildefines.h, or moving it up in the inclusion order if it was already included, in various places
- storage.c: make some variables only used in bli_builddir local to that
- storage.c: BLI_file_descriptor_size should allow 0 as a valid file descriptor
- path_util.c: make pointers to non-reentrant storage returned from folder routines const, necessitating making variables holding these returned pointers const elsewhere as well
- path_util.c: BLI_string_to_utf8 closes iconv context in case of conversion error
-  blf_lang.c: fill_locales routine now has its own "languages" local variable to construct paths (was stealing internal storage belonging to BLI_get_folder before)

source/blender/editors/space_file/space_file.c

@@ -629,7 +629,7 @@ void ED_spacetype_file(void)
 
 void ED_file_init(void)
 {
-	char *cfgdir = BLI_get_folder(BLENDER_USER_CONFIG, NULL);
+	const char * const cfgdir = BLI_get_folder(BLENDER_USER_CONFIG, NULL);
 	
 	fsmenu_read_system(fsmenu_get(), TRUE);