Subscript not shifted to left when base symbol is enclosed in brackets

**Describe the bug:**
The subscript is not shifted to the left to correct for italic, if the base symbol is enclosed in brackets.

**Expected behavior:**
I think `{V}_R` should render the same as `V_R`, as there is no semantic difference between the two. Maybe for groups of several symbols it makes sense, as in `{AV}_R`, although I'm not sure either.
This is especially important regarding computer-generated latex, where brackets are usually included even for single symbols.
This is the Mathjax behaviour.

**Screenshots:**

**Environment (please complete the following information):**
Tested in katex.org in various browsers