contact requests: clean image data handle invalid images

- Cleans cell's image data prior to usage/reusage.

- Only sets the contact request item cell's UIImage and hides the
  fallback avatar if it the image data exists and is correctly
  formed.

Change-Id: I3cd4c703ac33cee17157f2ccc86f6c54dc090a7e
Reviewed-by: Kateryna Kostiuk <kateryna.kostiuk@savoirfairelinux.com>

Ring/Ring/Features/ContactRequests/ContactRequestsViewController.swift

@@ -95,9 +95,12 @@ class ContactRequestsViewController: UIViewController, StoryboardBased, ViewMode
                     })
                     .disposed(by: cell.disposeBag)
 
+                // Set image if any
+                cell.fallbackAvatar.isHidden = false
+                cell.profileImageView.image = nil
                 if let imageData = item.profileImageData {
-                    cell.profileImageView.image = UIImage(data: imageData)
-                    if !imageData.isEmpty {
+                    if let image = UIImage(data: imageData) {
+                        cell.profileImageView.image = image
                         cell.fallbackAvatar.isHidden = true
                     }
                 }