put back 'return;' on empty terminal mode strings which was erroneously

removed in 3a6c6eeefe450a64e244ee39030938ddaacb8987

--HG--
extra : convert_revision : 75ed8083a683ebdb2fceca4a856d803fdeeb60af

svr-chansession.c

@@ -439,6 +439,7 @@ static void get_termmodes(struct ChanSess *chansess) {
 
 	if (len == 0) {
 		TRACE(("leave get_termmodes: empty terminal modes string"))
+		return;
 	}
 
 	while (((opcode = buf_getbyte(ses.payload)) != 0x00) && opcode <= 159) {