fixes crash when media url is empty

app/src/main/java/com/keylesspalace/tusky/StatusViewHolder.java

@@ -249,14 +249,23 @@ class StatusViewHolder extends RecyclerView.ViewHolder {
 
             previews[i].setVisibility(View.VISIBLE);
 
+            if(previewUrl == null || previewUrl.isEmpty()) {
+                Picasso.with(context)
+                        .load(mediaPreviewUnloadedId)
+                        .into(previews[i]);
+            } else {
                 Picasso.with(context)
                         .load(previewUrl)
                         .placeholder(mediaPreviewUnloadedId)
                         .into(previews[i]);
+            }
 
             final String url = attachments[i].url;
             final Status.MediaAttachment.Type type = attachments[i].type;
 
+            if(url == null || url.isEmpty()) {
+                previews[i].setOnClickListener(null);
+            } else {
                 previews[i].setOnClickListener(new View.OnClickListener() {
                     @Override
                     public void onClick(View v) {
@@ -265,6 +274,9 @@ class StatusViewHolder extends RecyclerView.ViewHolder {
                 });
             }
 
+
+        }
+
         if (sensitive) {
             sensitiveMediaWarning.setVisibility(View.VISIBLE);
             sensitiveMediaWarning.setOnClickListener(new View.OnClickListener() {