Merge pull request #578 in FS/freeswitch from…

Merge pull request #578 in FS/freeswitch from ~MARKL/freeswitch:bugfix/FS-8413-segfault-calling-session-getvariable-nil to master

* commit '6288af5e':
  FS-8413: Segfault calling session:getVariable(nil) in lua script

src/switch_channel.c

@@ -944,6 +944,7 @@ SWITCH_DECLARE(const char *) switch_channel_get_variable_dup(switch_channel_t *c
 
 	switch_mutex_lock(channel->profile_mutex);
 
+	if (!zstr(varname)) {
 		if (channel->scope_variables) {
 			switch_event_t *ep;
 
@@ -973,6 +974,7 @@ SWITCH_DECLARE(const char *) switch_channel_get_variable_dup(switch_channel_t *c
 				}
 			}
 		}
+	}
 
 	if (dup && v != vdup) {
 		if (v) {