Add only csv files in file explorer + avoid dirty exception if no file is chosen

load.py

@@ -49,7 +49,9 @@ def copy_waypoint(self=None):
     this.parent.update()
 
 def new_route(self=None):
-    filename = filedialog.askopenfilename()    # show an "Open" dialog box and return the path to the selected file
+    filename = filedialog.askopenfilename(filetypes = (("csv files", "*.csv"),))    # show an "Open" dialog box and return the path to the selected file
+
+    if filename.__len__() > 0:
         this.next_route = filename
 
         with open(filename, 'r') as csvfile: