Bad rendering for UPA

The [UPA](https://en.wikipedia.org/wiki/Uralic_Phonetic_Alphabet) sequence `i̯ᴖŋk͔ə̑m₍ᴢ̌́t` is not readable when rendered by Source Code Pro:


An UPA font renders it like this:


Found by rendering an [UPA test page](https://github.com/googlei18n/noto-source/blob/master/test/und-fonupa.html) with Source Code Pro. For more broken examples, compare [SourceCodePro-UPA.pdf](https://github.com/adobe-fonts/source-code-pro/files/668631/SourceCodePro-UPA.pdf) to [this](http://www.jltypes.com/Uvallanne/UvallanneTesti.pdf). Feel free to improve this test page, just send GitHub pull requests :-)