check that reddit_video_preview.fallback_url exists (fixes #255)

inc/processPostMedia.js

@@ -92,12 +92,20 @@ module.exports = function() {
             obj.has_media = true
             if(!gif_to_mp4) {
               if(post.preview) {
-                obj.media = {
-                  source: await downloadAndSave(post.preview.reddit_video_preview.fallback_url),
-                  height: post.preview.reddit_video_preview.height,
-                  width: post.preview.reddit_video_preview.width,
-                  duration: post.preview.reddit_video_preview.duration,
-                  is_gif: true
+                if(post.preview.reddit_video_preview) {
+                  if(post.preview.reddit_video_preview.fallback_url) {
+                    obj.media = {
+                      source: await downloadAndSave(post.preview.reddit_video_preview.fallback_url),
+                      height: post.preview.reddit_video_preview.height,
+                      width: post.preview.reddit_video_preview.width,
+                      duration: post.preview.reddit_video_preview.duration,
+                      is_gif: true
+                    }
+                  } else {
+                    obj.has_media = false
+                  }
+                } else {
+                  obj.has_media = false
                 }
               } else {
                 obj.has_media = false