[Glitch] Fix media modal crashing when media has no blurhash

Port 13206fcfb8 to glitch-soc

Signed-off-by: Claire <claire.github-309c@sitedethib.com>

app/javascript/flavours/glitch/features/ui/components/media_modal.js

@@ -231,10 +231,13 @@ class MediaModal extends ImmutablePureComponent {
   _sendBackgroundColor () {
     const { media, onChangeBackgroundColor } = this.props;
     const index = this.getIndex();
-    const backgroundColor = decodeRGB(decode83(media.getIn([index, 'blurhash']).slice(2, 6)));
+    const blurhash = media.getIn([index, 'blurhash']);
 
+    if (blurhash) {
+      const backgroundColor = decodeRGB(decode83(blurhash.slice(2, 6)));
       onChangeBackgroundColor(backgroundColor);
     }
+  }
 
   render () {
     const { media, statusId, intl, onClose } = this.props;