prevent error if playlist has no image

[scaphandroid]

Title

prevent error if playlist has no image

Related Issue

#2088

Motivation and Context

can use the tool even if spotify playlist is empty and avoir error in the case (particulary to automate download of a set of playlist where there can be empty playlist with no image)

How Has This Been Tested?

test with various empty and non empty playlist, no side effect detected

Types of Changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project
• My change requires a change to the documentation
• I have updated the documentation accordingly
• I have read the CONTRIBUTING document
• I have read the CORE VALUES document
• I have added tests to cover my changes
• All new and existing tests passed