[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:

app/post_metadata_test.go

@@ -1280,11 +1280,11 @@ func TestGetFirstLinkAndImages(t *testing.T) {
 			ExpectedFirstLink: "https://example.com",
 			ExpectedImages:    []string{"https://example.com/logo"},
 		},
-		"markdown links (not returned)": {
+		"markdown links": {
 			Input: `this is a [our page](http://example.com) and [another page][]
 
 [another page]: http://www.exaple.com/another_page`,
-			ExpectedFirstLink: "",
+			ExpectedFirstLink: "http://example.com",
 			ExpectedImages:    []string{},
 		},
 	} {