rfb/rfbproto: extend rfbCloseSocket() to prevent double closes

Specifically on Android newer 11, this would cause aborts by the fdsan
checker, see
https://developer.android.com/about/versions/11/behavior-changes-all#fdsan

It's also generally safer to mark a closed fd as closed as to not try to
re-use it.

Author: bk138

rfb/rfbproto.h

@@ -93,7 +93,7 @@ typedef int8_t rfbBool;
 #ifdef WIN32
 #define rfbSocket SOCKET
 #define RFB_INVALID_SOCKET INVALID_SOCKET
-#define rfbCloseSocket closesocket
+#define _rfbCloseSocket closesocket
 #else
 #ifdef LIBVNCSERVER_HAVE_SYS_TIME_H
 #include <sys/time.h>
@@ -104,13 +104,20 @@ typedef int8_t rfbBool;
 #define rfbSocket int
 #define SOCKET int /* LibVNCServer versions older than 0.9.13 defined this for non-Windows, so keep it here */
 #define RFB_INVALID_SOCKET (-1)
-#define rfbCloseSocket close
+#define _rfbCloseSocket close
 typedef int8_t rfbBool;
 #undef FALSE
 #define FALSE 0
 #undef TRUE
 #define TRUE -1
 #endif
+#define rfbCloseSocket(s)			\
+    {						\
+	if (s != RFB_INVALID_SOCKET) {		\
+	    _rfbCloseSocket(s);		\
+	    s = RFB_INVALID_SOCKET;		\
+	}					\
+    }
 
 typedef uint32_t rfbKeySym;
 typedef uint32_t rfbPixel;