[poppler] Fix crash in 1026.asan.0.42.pdf

[Albert Astals Cid]

Hi guys, i've got more "secret files" crashers. This patch files a crash in 
one called 1026.asan.0.42.pdf

Thomas, guys, can you verify it makes sense? It makes to me, but more eyes 
better.

Cheers,
  Albert

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