Make sure we do not allocate new edge when talking to old nodes and the same edge already exists

When tinc gets ADD_EDGE from older versions it will allocate
new edge in protocol_edge.c:189 due to missed case in lines 149-171 where
local_address is not defined.

src/protocol_edge.c

@@ -167,6 +167,8 @@ bool add_edge_h(connection_t *c, const char *request) {
 				if(!tunnelserver)
 					forward_request(c, request);
 
+				return true;
+			} else {
 				return true;
 			}
 		} else {