Android runtime: Cannot open experiment if pool filenames contain special characters

[smathot]

No error is visible in the debug output, but android.py logcat gives the following stacktrace:

I/python  (16037): Traceback (most recent call last):
I/python  (16037):   File "start.pyx", line 55, in start (jni/../jni/application/src//start.c:1352)
I/python  (16037):   File "opensesame/main.py", line 108, in main
I/python  (16037):   File "opensesame/libopensesame/experiment.py", line 204, in __init__
I/python  (16037):   File "opensesame/libopensesame/experiment.py", line 622, in open
I/python  (16037): UnicodeEncodeError: 'ascii' codec can't encode characters in position 68-69: ordinal not in range(128)