Refactor charging function

[dementive]

• Removed the else from the top level of the charging() function, the logic is the same but slightly easier to read now.

• Use if not x.exists() in the charging() function before opening the file instead of FileNotFoundError exceptions, makes the function a lot easier to read.

• Close the power_supply_type_path after reading the supply_type as it is not used later.

• Remove else: continue from the end of the charging() function for loop, this didn't actually do anything.

I tested the charging() function on my laptop plugged in and plugged out and it is still working as expected with these changes.

[AdnanHodzic]

LGTM! Thank you for your contribution, you will be credited for your work as part of future release.