Fix Chrome issue with sizes="0px" (#7886)

"Do not dumb here. Not dumb area here."

app/javascript/mastodon/components/media_gallery.js

@@ -122,7 +122,7 @@ class Item extends React.PureComponent {
       const hasSize = typeof originalWidth === 'number' && typeof previewWidth === 'number';
 
       const srcSet = hasSize ? `${originalUrl} ${originalWidth}w, ${previewUrl} ${previewWidth}w` : null;
-      const sizes  = hasSize ? `${displayWidth * (width / 100)}px` : null;
+      const sizes  = hasSize && (displayWidth > 0) ? `${displayWidth * (width / 100)}px` : null;
 
       const focusX = attachment.getIn(['meta', 'focus', 'x']) || 0;
       const focusY = attachment.getIn(['meta', 'focus', 'y']) || 0;