DS Parser not providing useful feedback in stepping mode

[stroomdev00]

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If a DS Parser reaches a record that doesn't match its expected format at the top level it jumps past that record and shows the output for the next matching record along with an ERROR: 1 message on the RHS with no further detail as to where the problem lies.

For example, record 12 is invalid. Stepping at record 11 works as expected, stepping to the next record actually displays record 13 but states it's record 12 - subsequent records numbers are offset by 1, e.g. record 20 is stated as <streamId>:<partId>:19

I'd expect the stepping to either stop and display either the invalid record 12 or (as in previous versions) display both records 12 and 13 in the source. Either way, we need an error message to say why it doesn't match.