to_xml generates invalid xml for arrays of namespaced ActiveRecords

The problem is similar to the one described in:

#2723 to_xml generates invalid xml with namespaced ActiveRecord

That patch applied to a single ActiveRecord with namespaces. It turns out that the same problem occurs in arrays of ActiveRecords with namespaces as well, e. g., those returned by find(:all).

The prior patch fixed options[:root] in to_xml for ActiveRecords . However, if the ActiveRecords are in an array, then the value of options[:root] is set in in activesupport/lib/active_support/core_ext/array/conversions.rb to_xml method and passed in to activemodel/lib/active_model/serializers/xml.rb and it contains invalid xml characters. Since options[:root] is not nil, the prior patch has no effect on correcting the invalid characters in arrays of namespaced ActiveRecords.

This patch strips out the invalid characters for any classes with namespaces from the root set in the array to_xml method.