Fix a crash that could occur when handing device state changes.

When the state of a device changes, the device state thread tells the extension
state handling code that it changed.  Then, the extension state code calls the
callback in chan_sip so that it can update subscriptions to that extension.
A pointer to a sip_pvt structure is passed to this function as the call which
needs a NOTIFY sent.  However, there was no locking done to ensure that the pvt
struct didn't disappear during this process.
(issue #9946, reported by tdonahue, patch by me, patch updated to trunk to use
 the sip_pvt lock wrappers by eliel)


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@69944 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -8281,6 +8281,8 @@ static int cb_extensionstate(char *context, char* exten, int state, void *data)
 {
 	struct sip_pvt *p = data;
 
+	ast_mutex_lock(&p->lock);
+
 	switch(state) {
 	case AST_EXTENSION_DEACTIVATED:	/* Retry after a while */
 	case AST_EXTENSION_REMOVED:	/* Extension is gone */
@@ -8301,6 +8303,9 @@ static int cb_extensionstate(char *context, char* exten, int state, void *data)
 
 	if (option_verbose > 1)
 		ast_verbose(VERBOSE_PREFIX_1 "Extension Changed %s new state %s for Notify User %s\n", exten, ast_extension_state2str(state), p->username);
+	
+	ast_mutex_unlock(&p->lock);
+
 	return 0;
 }