winsyslog: prevent buffer overrun on when copying formatted strings

The Windows vsyslog emulation is somewhat archaic and assumes that
the log line while max out at 1024 characters, which is not the
case nowadays. Using vsnprintf instead vsprintf, will truncate the
copy instead of writing outside the buffer.

Change-Id: I6a6176fd79eeaf663d2cb9396715babe5254a6e2

src/winsyslog.c

@@ -83,7 +83,7 @@ void closelog(void)
     CONST CHAR *arr[1];
     char tmp[1024];
 
-    vsprintf(tmp, format, arglist);
+    vsnprintf(tmp, 1024, format, arglist);
 
 #ifndef RING_UWP
     arr[0] = tmp;