[3.15] gh-75595: Do not save a blank int entry in IDLE Settings (GH-152743) (#152827)

[3.15] gh-75595: Do not save a blank int entry in IDLE Settings (GH-152743) (#152827)

gh-75595: Do not save a blank int entry in IDLE Settings (GH-152743)

gh-83653: Do not save a blank int entry in IDLE Settings

Blanking an integer entry wrote an empty string to the config file, which
caused an "invalid int value" warning when it was read back.
(cherry picked from commit 3428762f33c6c064998f5b0c385cdfd0f0c2e198)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
Co-authored-by: Cheryl Sabella <cheryl.sabella@gmail.com>