Application says that feed is invalid, while W3C says the inverse

[metal3d]

Describe the bug
A clear and concise description of what the bug is.
Opening my rss feed: https://www.metal3d.org/index.xml

But W3C says that it's ok:
https://validator.w3.org/feed/check.cgi?url=https%3A%2F%2Fwww.metal3d.org%2Findex.xml

To Reproduce
Steps to reproduce the behavior:
1.Add my feed
2. see error

Expected behavior
The feed should be displayed

Platform (please complete the following information):

• OS: [e.g. Fedora 33]
• Version [e.g. 0.9.0]

[yang991178]

It seems that the regular expression parsing XML encoding lacks a greedy modifier. Will fix in the next release.

XML_ENCODING_RE = /^<\?xml.+encoding="(.+)".*?\?>/i // problematic
XML_ENCODING_RE = /^<\?xml.+encoding="(.+?)".*?\?>/i // correct