[uforead] parse multiple attrs in xmlNode

[kaydeearts]

This is to fix #1673 #1669

@frankrolf can you review & confirm this fixes the issue? I've attached the new output font and ran the test script:

ufo-advance-height-weight.otf
{'.notdef': (100, 0), 'space': (200, 0), 'A': (400, 47)}

ufo-advance-height-weight.otf.zip

Checklist:

• I have followed the [Contribution Guidelines](https://github.com/adobe-type
  -tools/afdko/blob/develop/CONTRIBUTING.md)
• I have added test code and data to prove that my code functions correctly
• I have verified that new and existing tests pass locally with my changes
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation

[skef]

looks good to me

[frankrolf]

Thank you for fixing this! I have no idea to test the PR locally, but I am grateful anyway :-)