[MM-29224] Fix bug where markdown image link doesn't show preview (#15862)

* Fix bug where markdown image has no preview

* go fmt

* Fix failing test

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

app/post_metadata.go

@@ -316,6 +316,10 @@ func getFirstLinkAndImages(str string) (string, []string) {
 			if firstLink == "" {
 				firstLink = v.Destination()
 			}
+		case *markdown.InlineLink:
+			if firstLink == "" {
+				firstLink = v.Destination()
+			}
 		case *markdown.InlineImage:
 			images = append(images, v.Destination())
 		case *markdown.ReferenceImage: