Pressure canning stock
In any food safety situation you really must ultimately ask yourself 3 questions to determine relative safety:

How High of a temperature am I sure I achieved?

How long did I hold this temperature?

How well sealed is the container?

If you are pressure canning, there are reasonably good chances you kept VERY high pressure and temperature. As for time, I cannot say.

For years my grandparents, my parents and myself have canned vegetables, soups, stocks, etc. and only rarely did we have errors because of some content of food. Most of our spoilage came from broken seals.

If you're confident in your canning technique, I see no reason why some egg white would hurt your stock. It's an animal protein just like any other.