Increment offset in the loop when reading _NET_WORKAREA

Previously, if there was more than one work area, this would be
an infinite loop, re-reading the first workarea repeatedly.

Reported by Ragnarok (thanks!)

src/conio/x_events.c

@@ -243,6 +243,8 @@ x11_get_maxsize(int *w, int *h)
 				break;
 			if (atr != XA_CARDINAL)
 				break;
+			if (nir > 0)
+				offset += nir;
 			ret = (long *)prop;
 			if (nir >= 3) {
 				if (ret[2] > maxw)