v4-beta.3: spacing around sqcup sometimes asymmetrical

[pkra]

Apologies for not having a good minimal example.

Take something like $$ \vcenter{\img[][16pt][16pt][]{some.svg}} \sqcup \vcenter{\img[][30pt][30pt][]{another.svg}} \sqcup \vcenter{\img[][58pt][58pt][]{yetanother.svg}} .$$ (using mathjax-img).

In v3, the spacing around \sqcup would be symmetrical:

In v4, the space is asymmetrical:

[dpvc]

I've made a PR to fix this.

[pkra]

I've tested the patch - thank you!