read_save: checking file extension is different

[huni1023]

in read_save.py, there are bunch of method checking file extension.

while in the method save_pkl line 16 checking extension with directly slicing string, the method read_yaml line 26 checking extension with os.path.splitext.

for consistency, using unified method to checking file extension is required.

** in pandize_folder, the extension means string without dot. but in save_pkl the extension contains dot.

[huni1023]

unite extension checking method to endswith: 82ec5bc