Fix ActionMode invalidation in onLongClick callbacks

Description

This fixes long press interactions where an ActionMode is already in progress.

The if (actionMode == null) startActionMode() else invalidateActionMode() pattern is already present in the codebase at multiple location, so I suppose this was just an oversight.

Before	After
15-54-30.4318343	15-55-12.0827028

Types of changes

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

Checklist

• I have read the CONTRIBUTING section of the README document.