An air taxi flight crew failed to note the hold short lines protecting the approach path for Runway 17L at LBB and taxied through it.

Narrative

I received a taxi clearance from Ground Control to taxi via Taxiway Juliet to Runway 26 and to cross Runway 35L. After crossing Runway 35L and taxiing down Juliet I started my 'before takeoff brief.' I looked up just in time to see a hold short line that I was crossing. I continued taxiing clear of the runway and looked to read what the red and white hold short sign said; that I had passed it read '17apr.' Neither Ground Control nor Tower said anything to me about the incursion. We have a 'safe taxi' display however it doesn't show that there is a hold short line there on Juliet at 17L-35R. On the airport diagram page it doesn't show that 17L-35R and Taxiway Juliet are connected; but they are and there is a hold short line and a red and white sign there. I failed to stay heads up and to refrain from doing a crew brief while I was taxiing. I do take the time to brief the taxi and to discuss any runways that will be crossed from the airport diagram chart and I keep the 'safe taxi' display up during the taxi on each flight. However; this time it did not keep me from doing something I vowed I would never do.