Avoid failing when embedding with a Window id of 0

I'd like to let st run with its own window when trying to embed it to a window with id 0 instead of exiting with an error.

st.c

@@ -3136,8 +3136,8 @@ xinit(void) {
 		| ButtonMotionMask | ButtonPressMask | ButtonReleaseMask;
 	xw.attrs.colormap = xw.cmap;
 
-	parent = opt_embed ? strtol(opt_embed, NULL, 0) : \
-			XRootWindow(xw.dpy, xw.scr);
+	if (!(opt_embed && (parent = strtol(opt_embed, NULL, 0))))
+		parent = XRootWindow(xw.dpy, xw.scr);
 	xw.win = XCreateWindow(xw.dpy, parent, xw.l, xw.t,
 			xw.w, xw.h, 0, XDefaultDepth(xw.dpy, xw.scr), InputOutput,
 			xw.vis, CWBackPixel | CWBorderPixel | CWBitGravity