undo: remove the added magic line when a replacement caused one

This fixes https://savannah.gnu.org/bugs/?59796.

Bug existed since before version 2.2.4.

src/text.c

@@ -583,6 +583,8 @@ void do_undo(void)
 		break;
 	case REPLACE:
 		undidmsg = _("replacement");
+		if ((u->xflags & INCLUDED_LAST_LINE) && !ISSET(NO_NEWLINES))
+			remove_magicline();
 		data = u->strdata;
 		u->strdata = line->data;
 		line->data = data;
@@ -755,6 +757,8 @@ void do_redo(void)
 		break;
 	case REPLACE:
 		redidmsg = _("replacement");
+		if ((u->xflags & INCLUDED_LAST_LINE) && !ISSET(NO_NEWLINES))
+			new_magicline();
 		data = u->strdata;
 		u->strdata = line->data;
 		line->data = data;
@@ -1039,6 +1043,8 @@ void add_undo(undo_type action, const char *message)
 		break;
 	case REPLACE:
 		u->strdata = copy_of(thisline->data);
+		if (thisline == openfile->filebot && u->strdata[0] != '\0')
+			u->xflags |= INCLUDED_LAST_LINE;
 		break;
 #ifdef ENABLE_WRAPPING
 	case SPLIT_BEGIN: