fixes a crash in build.bat when the 'dist' folder did not exist

- The error was:
    Traceback (most recent call last):
      File setup.py, line 61, in <module>
	create_windows_exe()
      File setup.py, line 13, in create_windows_exe
	[os.remove(x) for x in get_file_paths('dist')]
      File setup.py, line 10, in get_file_paths
	file_paths = [f for f in listdir(folder_name) if isfile(join(folder_name, f))]
    FileNotFoundError: [WinError 3] The system cannot find the path specified: 'dist'

- The error occured only on first checkout; once the dist folder was
  built this error did not occur.

Author: dalpert-korewireless

setup.py

@@ -7,8 +7,11 @@ def create_windows_exe():
 
     # Get theme files and store them in a list
     def get_file_paths(folder_name):
-        file_paths = [f for f in listdir(folder_name) if isfile(join(folder_name, f))]
-        return ['{}/{}'.format(folder_name, i) for i in file_paths]
+        if os.path.isdir(folder_name):
+            file_paths = [f for f in listdir(folder_name) if isfile(join(folder_name, f))]
+            return ['{}/{}'.format(folder_name, i) for i in file_paths]
+        else:
+            return []
 
     [os.remove(x) for x in get_file_paths('dist')]
     theme_file_paths = get_file_paths("Themes")