Avoid calling GetMaster() with old Xorg
GetMaster() wasn't exported until Xorg 1.18 so it is unsafe to use
from libvnc.so for older versions.
diff --git a/unix/xserver/hw/vnc/InputXKB.c b/unix/xserver/hw/vnc/InputXKB.c
index 490d6d1..2a3f7af 100644
--- a/unix/xserver/hw/vnc/InputXKB.c
+++ b/unix/xserver/hw/vnc/InputXKB.c
@@ -42,6 +42,10 @@
#define KEYBOARD_OR_FLOAT MASTER_KEYBOARD
#endif
+#if XORG < 118
+#define GetMaster(dev, type) ((dev)->master)
+#endif
+
extern DeviceIntPtr vncKeyboardDev;
static void vncXkbProcessDeviceEvent(int screenNum,