pdftoppm/pdftocairo: Fix -e/-o printing the wrong pages

Fixes #873
6 jobs for fix_873 in 4 minutes and 44 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #1336042
build

00:03:11

passed #1336047
build_android

00:01:27

passed #1336043
build_clang_libcpp

00:03:19

passed #1336046
build_clazy

00:04:41

passed #1336045
build_mingw64_fedora

00:03:20

passed #1336044
build_ubuntu_16_04

00:01:36