devdraw: fix x11 input

R=rsc
https://codereview.appspot.com/10458043

src/cmd/devdraw/x11-itrans.c

diff --git a/src/cmd/devdraw/x11-itrans.c b/src/cmd/devdraw/x11-itrans.c
index 4eac847..d84cdc8 100644
--- a/src/cmd/devdraw/x11-itrans.c
+++ b/src/cmd/devdraw/x11-itrans.c
@@ -153,7 +153,7 @@
 	Rune r;
 
 	r = __xtoplan9kbd(e);
-	if(r < 0)
+	if(r == -1)
 		return nil;
 	return sendrune(r);
 }