manage: For isfloating/oldstate check/set, ensure trans client actually exists

In certain instances trans may be set to a window that doesn't actually
map to a client via wintoclient; in this case it doesn't make sense
to set isfloating/oldstate since trans is essentially invalid in that
case / correlates to the above condition check where trans is set /
XGetTransientForHint is called.

dwm.c

@@ -1064,7 +1064,7 @@ manage(Window w, XWindowAttributes *wa)
 	XSelectInput(dpy, w, EnterWindowMask|FocusChangeMask|PropertyChangeMask|StructureNotifyMask);
 	grabbuttons(c, 0);
 	if (!c->isfloating)
-		c->isfloating = c->oldstate = trans != None || c->isfixed;
+		c->isfloating = c->oldstate = t || c->isfixed;
 	if (c->isfloating)
 		XRaiseWindow(dpy, c->win);
 	attach(c);