Only call completion() on main thread if SwiftLinkPreview.preview() was called from main thread
Only call completion() on main thread if SwiftLinkPreview.preview() was called from main thread

This enables the entire process to be performed in the background

LeonardoCardoso/SwiftLinkPreview,LeonardoCardoso/SwiftLinkPreview,LeonardoCardoso/SwiftLinkPreview,LeonardoCardoso/SwiftLinkPreview