Not a definitive answer...
This actually happened in the game I played today. On the next to last turn, all 4 civ cards were bought. There were only 4 cards left in the draw pile. Enough to fill the display, but no cards left in the draw pile. One of the cards was the 'draw an extra civ card' card. (ick, that sounds funny in my head). The display was full, so we played another turn. We just assumed that card did nothing and the only reason to get it was for the end of game scoring bottom part.
According to the rulebook, that would be the correct way to play it