Fix invalid column name breaking the whole search

[mad201802]

Description

When specifically selecting a column name that doesnt exist in one ofe the selected tables, the command fails and doesnt print any results even if there are some.

Ex.: `db-tool grep -

Definition of Done

The bug should be fixed lol

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Problem

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Solution

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[mad201802]

Thats a tricky problem to solve ... we need to parse the vc argument and check if the colum exists in that table.