Fix footnote dialog height

The paginator is now layout contained after johnfactotum/foliate-js@b7ff640

src/reader/reader.html

@@ -111,6 +111,7 @@
 }
 #footnote-dialog main {
     min-height: 0;
+    flex: 1
 }
 @media (max-width: 500px) {
     #footnote-dialog {