ccl_chromium_cache - handle malformed simplecache data better #39
Description
We have introduced a lot of error handling for blockfile cache data, but SimpleCache is quite fragile still.
We should check for empty (0 byte) files ahaead of trying to load them, and handle exceptions (likely in the ChromiumSimpleFileCache._build_keys function, as this touches most of the data).
Related to issue #38 as we should be raising and catching more specific exeptions.