Update lib/backports/3.2.0/enumerator/product.rb

Let's not go out of our way to return senseless results.
See ruby/spec#1140

lib/backports/3.2.0/enumerator/product.rb

@@ -56,7 +56,7 @@ def size
       @__enums.each do |enum|
         return nil unless enum.respond_to?(:size)
         size = enum.size
-        return size if size == nil || size == Float::INFINITY || size == -Float::INFINITY
+        return size if size == nil || size == Float::INFINITY
         return nil unless size.kind_of?(Integer)
         total_size *= size
       end