Support not having a space after a dollar sign closing a LaTeX block

[postmath]

This often occurs in text such as in the $n$th iteration, .... To reproduce:

In the $n$th iteration, the size is $\frac{2}{3}$.

Expected result:

In the $n$th iteration, the size is $\frac{2}{3}$.

Actual result:

In the $n\$thiteration,thesizeis$ \frac{2}{3}$.

(Note: github requires starting the LaTeX block with dollar-backtick and ending it with backtick-dollar in this situation. Another implementation, stackedit.io, accepts this syntax without backticks; if you do include them, they get rendered.)