[varLib_instancer - updateNameRecords] Allow NameRecord that do not exist for an platform

[moi15moi]

Problem that this PR solve

When updating namerecord, allow an NameRecord that do not exist for an platform.

Example of an case where this PR is usefull

When trying to instantiateVariableFont with the font Bahnschrift, an exception is raised.

from fontTools import ttLib
from fontTools.ttLib.tables._f_v_a_r import NamedInstance
from fontTools.varLib import instancer
from typing import List

fontCollection = ttLib.TTCollection()
font = ttLib.TTFont("BAHNSCHRIFT.TTF")
instances: List[NamedInstance] = font["fvar"].instances

for instance in instances:
    generatedFont = instancer.instantiateVariableFont(font, instance.coordinates,  updateFontNames=True)
    fontCollection.fonts.append(generatedFont)

savePath = "BAHNSCHRIFT.ttc"
fontCollection.save(savePath)

It append because the platform 1 doesn't have the nameID that the stat table use.
So, when it try to getName, it return None which raise an exception.

In order not to raise the exception, we catch it and set the variable to None. Like that, we can instantiate our variable font without problem.