When extracting a folder name from the byte slices used as database
keys, bytes.IndexByte() is used to find and remove trailing 0 bytes.
In case the folder name is 64 bytes long, bytes.IndexByte() returns
-1. Before this change, syncthing crashed in this case with an
out-of-bounds slice access.
The commit fixes the problem and also introduces a test case which
checks for the presence of the bug.
Jakob Borg
Jochen Voss