Multi corpus selection with conflicting segmentation should default to tokens

[amir-zeldes]

If multiple corpora are selected whose corpus properties specify different segmentations are selected, results from corpora missing the selected segmentation cause the result list to get stuck. To reproduce:

• select besa.letters and coptic.treebank
• search for pos="ACOND"

See for example:
https://corpling.uis.georgetown.edu/annis/#_q=cG9zPSJBQ09ORCI&_c=YmVzYS5sZXR0ZXJzLGNvcHRpYy50cmVlYmFuaw&cl=5&cr=5&s=0&l=10&_bt=bm9ybV9ncm91cA

Note that switching base text to "tokens" and hitting refresh resolves the problem. The behavior of switching to "tokens" should happen by default (since it is impossible to display using a different segmentation whenever there are results from a corpus that does not support that segmentation).

[thomaskrause]

This seems to be fixed. When selecting multiple corpora (e.g. besa.letters and Ridges) the "Show context in" field in the search option is reset to "tokens".