[NTG-context] Odd behaviour with Plex typescript

[Max Chernoff]

If you load the Plex typescript, a spurious space is added on the first
switch to another font, messing up any alignment. This doesn't happen
with any other fonts; only with Plex.

MWE:

     \setuphead[section][style={\switchtobodyfont[modern]}]
     \setupbodyfont[plex]

     \starttext
         \section{A}
         A
     \stoptext

I was able to fix this by removing the space immediately before the "%"
on line 136 of "type-imp-plex.mkiv", changing it from this (original):

         \definefontfeature[plexwideneddefault][default][extend=\luaexpr{1/0.85}] % An odd floating point number to correct monospace.

to this (fixed):

         \definefontfeature[plexwideneddefault][default][extend=\luaexpr{1/0.85}]% An odd floating point number to correct monospace.

I'm pretty sure that TeX is ignoring spaces at this point, so I have no
idea why this issue exists or why the fix works.

-- Max