Make sure fallback block handler remains enabled
Commit f8e3b34 introduced a regression where the fallback write block
handler would cease working after the first time it was called,
potentially stalling writes.
diff --git a/unix/xserver/hw/vnc/vncBlockHandler.c b/unix/xserver/hw/vnc/vncBlockHandler.c
index c9a7428..4e44478 100644
--- a/unix/xserver/hw/vnc/vncBlockHandler.c
+++ b/unix/xserver/hw/vnc/vncBlockHandler.c
@@ -104,6 +104,9 @@
FD_ZERO(&fallbackFds);
vncWriteBlockHandler(&fallbackFds);
+ // vncWriteBlockHandler() will clear this, so we need to restore it
+ needFallback = TRUE;
+
if (!XFD_ANYSET(&fallbackFds))
return;