display: show the cursor during suspension also when built with Slang

This fixes https://savannah.gnu.org/bugs/?57517.

Bug existed since version 2.9.0.

src/nano.c

@@ -1213,6 +1213,7 @@ RETSIGTYPE do_suspend(int signal)
 
 	/* Move the cursor to the last line of the screen. */
 	move(LINES - 1, 0);
+	curs_set(1);
 	endwin();
 
 	/* Display our helpful message. */