live555: fix build with versions >= 2024.11.28

In the 2024.11.28 release (version 1732752000), live555 introduced
`EventLoopWatchVariable` as a typedef for `std::atomic<char>`, replacing
direct use of `char` in earlier versions. Add a conditional typedef to
define it as `char` for older versions, and update `event_rtsp` and
`event_data` to use `EventLoopWatchVariable`.

modules/access/live555.cpp

@@ -194,6 +194,10 @@ class RTSPClientVlc;
 #define CAP_SUBSESSION_PAUSE    (1 << 3)
 #define CAPS_DEFAULT            CAP_RATE_CONTROL
 
+#if LIVEMEDIA_LIBRARY_VERSION_INT < 1732752000 // 2024.11.28
+typedef char EventLoopWatchVariable;
+#endif
+
 struct demux_sys_t
 {
     char            *p_sdp;    /* XXX mallocated */
@@ -232,8 +236,8 @@ struct demux_sys_t
     bool             b_no_data;     /* if we never received any data */
     int              i_no_data_ti;  /* consecutive number of TaskInterrupt */
 
-    char             event_rtsp;
-    char             event_data;
+    EventLoopWatchVariable event_rtsp;
+    EventLoopWatchVariable event_data;
 
     bool             b_get_param;   /* Does the server support GET_PARAMETER */
     bool             b_paused;      /* Are we paused? */