Yup - it's right there on page 6 of the standard Dip rules:
http://www.wizards.com/avalonhill/rules/diplomacy.pdf
A standoff does not dislodge a unit already in the province where the standoff took place. If two units (or forces of equal strength) attack the same province, thus standing each other off, a unit already in that province is not dislodged.
So, based on that, the army in Galicia remains unaffected by the Austrian attack and its support for the German attack should remain in place.