manage: Make sure c->isfixed is applied before floating checks

Commit 8806b6e23793 ("manage: propertynotify: Reduce cost of unused size
hints") mistakenly removed an early size hints update that's needed to
populate c->isfixed for floating checks at manage() time. This resulted
in fixed (size hint min dimensions == max dimensions) subset of windows
not floating when they should.

See https://lists.suckless.org/dev/2204/34730.html for discussion.

Ref.
https://git.suckless.org/dwm/commit/8b48e309735f5fe49d35f86e967f4b5dea2a2f2d.html

dwm.c

@@ -2395,6 +2395,7 @@ manage(Window w, XWindowAttributes *wa)
 		XSetWindowBorder(dpy, w, scheme[SchemeNorm][ColBorder].pixel);
 	#endif // BAR_FLEXWINTITLE_PATCH
 	configure(c); /* propagates border_width, if size doesn't change */
+	updatesizehints(c);
 	if (getatomprop(c, netatom[NetWMState]) == netatom[NetWMFullscreen])
 		setfullscreen(c, 1);
 	updatewmhints(c);