'Undefined offset:' notices in loca and htmx classes

[mondrake]

In the test suite of a Drupal module that uses this library (https://www.drupal.org/pift-ci-job/610235), I am getting a lot of PHP notices for undefined offset like

exception: [Notice] Line 46 of vendor/phenx/php-font-lib/src/FontLib/Table/Type/loca.php:
Undefined offset: 2144
....
exception: [Notice] Line 30 of vendor/phenx/php-font-lib/src/FontLib/Table/Type/hmtx.php:
Undefined offset: 5332

exception: [Notice] Line 31 of vendor/phenx/php-font-lib/src/FontLib/Table/Type/hmtx.php:
Undefined offset: 5333

I am not sure how to fix this, but checking the existence of the array element seems to me a right thing to do anyway