Reinstate dm_83 playback support if no extension given

VET 2.60b allegedly still allows them so we can too I guess. You could in theory also use ETe now to up-convert to 84 using the record while playing back feature.

src/qcommon/common.c

@@ -40,7 +40,7 @@ If you have questions concerning this license or the applicable additional terms
 
 #include "../client/keys.h"
 
-const int demo_protocols[] = { OLD_PROTOCOL_VERSION, NEW_PROTOCOL_VERSION, 0 };
+const int demo_protocols[] = { VERY_OLD_PROTOCOL_VERSION, OLD_PROTOCOL_VERSION, NEW_PROTOCOL_VERSION, 0 };
 
 #define USE_MULTI_SEGMENT // allocate additional zone segments on demand
 

src/qcommon/qcommon.h

@@ -311,6 +311,7 @@ You or the server may be running older versions of the game. Press the auto-upda
 // 2.4 - protocol 80
 // 1.33 - protocol 59
 // 1.4 - protocol 60
+#define VERY_OLD_PROTOCOL_VERSION 83
 #define	OLD_PROTOCOL_VERSION	84
 
 // new protocol with UDP spoofing protection: