fix(ruby): handle unknown attributes in index_exists (#4231)

Author: millotp

templates/ruby/search_helpers.mustache

@@ -396,11 +396,13 @@ end
 def index_exists?(index_name)
   begin
     get_settings(index_name)
-  rescue AlgoliaHttpError => e
-    return false if e.code == 404
+  rescue Exception => e
+    if e.is_a?(AlgoliaHttpError)
+      return false if e.code == 404
 
-    raise e
+      raise e
+    end
   end
 
   true
-end
+end