fix crashes during resizing

- safeguard ncurses functions called within resize handler
- stop refresh_layout from being called while directories are loading
- resolves #20

ext/sncurses.c

@@ -16,6 +16,24 @@ sinit_pair(short pair, short f, short b)
 	return r;
 }
 
+int
+sendwin(void)
+{
+	pthread_mutex_lock(&ncurses_lock);
+	int r = endwin();
+	pthread_mutex_unlock(&ncurses_lock);
+	return r;
+}
+
+int
+srefresh(void)
+{
+	pthread_mutex_lock(&ncurses_lock);
+	int r = refresh();
+	pthread_mutex_unlock(&ncurses_lock);
+	return r;
+}
+
 WINDOW *
 snewwin(int nlines, int ncols, int begin_y, int begin_x)
 {

ext/sncurses.h

@@ -3,6 +3,8 @@
 #include <ncurses.h>
 
 int sinit_pair(short pair, short f, short b);
+int sendwin(void);
+int srefresh(void);
 WINDOW *snewwin(int nlines, int ncols, int begin_y, int begin_x);
 int sdelwin(WINDOW *win);
 int sbox(WINDOW *win, chtype verch, chtype horch);

fuf.c

@@ -51,15 +51,18 @@ char preview_path[PATH_MAX];
 static void
 handle_redraw()
 {
-	endwin();
-	refresh();
+	sendwin();
+	srefresh();
 
 	/* keep the file list within resized window */
 	scroll_pos = items_len-1 > scroll_pos-LINES+2 
 		? items_len-1-LINES+2 : items_len-scroll_pos < LINES+2 
 		? 0 : scroll_pos;
 
-	refresh_layout();
+	extern bool items_loading;
+	if (!items_loading) {
+		refresh_layout();
+	}
 }
 
 static void