fix various bugs related to list handling of channel variables (issue #5548)

use nolock lists for channel variables, since no locks are needed (these lists are either temporary or protected by the channel's own lock)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@6900 65c4cc65-6c06-0410-ace0-fbb531ad65f3

include/asterisk/linkedlists.h

@@ -369,6 +369,8 @@ struct {								\
 #define AST_LIST_INSERT_HEAD(head, elm, field) do {			\
 		(elm)->field.next = (head)->first;			\
 		(head)->first = (elm);					\
+		if (!(head)->last)					\
+			(head)->last = (elm);				\
 } while (0)
 
 /*!