fix BadMatch error when embedding on some windows

When embedded, st fails with BadMatch error if the embedder's window has
non-default colormap/depth/visual.  This commit fixes that by creating
st's window inside root and then reparent it into embedder.

The reference window for dc.gc is also changed to match root's visuals.

A similar commit had been made for dmenu[1].
See this issue[2] on github for context.

[1]: https://git.suckless.org/dmenu/commit/0fe460dbd469a1d5b6a7140d0e1801935e4a923b.html
[2]: https://github.com/phillbush/xfiles/issues/47

x.c

@@ -1131,7 +1131,7 @@ xinit(int cols, int rows)
 {
 	XGCValues gcvalues;
 	Cursor cursor;
-	Window parent;
+	Window parent, root;
 	pid_t thispid = getpid();
 	XColor xmousefg, xmousebg;
 
@@ -1168,16 +1168,19 @@ xinit(int cols, int rows)
 		| ButtonMotionMask | ButtonPressMask | ButtonReleaseMask;
 	xw.attrs.colormap = xw.cmap;
 
+	root = 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,
+		parent = root;
+	xw.win = XCreateWindow(xw.dpy, root, xw.l, xw.t,
 			win.w, win.h, 0, XDefaultDepth(xw.dpy, xw.scr), InputOutput,
 			xw.vis, CWBackPixel | CWBorderPixel | CWBitGravity
 			| CWEventMask | CWColormap, &xw.attrs);
+	if (parent != root)
+		XReparentWindow(xw.dpy, xw.win, parent, xw.l, xw.t);
 
 	memset(&gcvalues, 0, sizeof(gcvalues));
 	gcvalues.graphics_exposures = False;
-	dc.gc = XCreateGC(xw.dpy, parent, GCGraphicsExposures,
+	dc.gc = XCreateGC(xw.dpy, xw.win, GCGraphicsExposures,
 			&gcvalues);
 	xw.buf = XCreatePixmap(xw.dpy, xw.win, win.w, win.h,
 			DefaultDepth(xw.dpy, xw.scr));