7435: Media Editor error if Path value was changed to a non existing file

gramps/gui/editors/editmedia.py

@@ -297,7 +297,17 @@ class EditMedia(EditPrimary):
             return
         
         path = self.file_path.get_text()
-        self.determine_mime()
+        if os.path.isfile(path):                                           
+            self.determine_mime()                                          
+        else:                                                              
+            msg1 = _("There is no media matching the current path value!") 
+            msg2 = _("You have attempted to use the path with "            
+                            "value '%(path)s'. This path does not exist!"     
+                            " Please enter a different path") % {             
+                            'path' : path }                                   
+            ErrorDialog(msg1, msg2)                                    
+            self.ok_button.set_sensitive(True)                             
+            return                                                         
 
         self.obj.set_path(get_unicode_path_from_file_chooser(path))