base: Improve errors for failures to parse
Created by: bjackman
Some events from the kernel cannot be parsed by old trace-cmd binaries. This results in data_str starting with "[FAILED TO PARSE]", which we ourselves fail to parse because we expect to find a key=value pair.
This adds a missing 'continue' statement to avoid attempting to avoid a KeyError when attempting to use an unset prev_key as a key into data_dict, and also adds a special error for the "[FAILED TO PARSE]" case.