pdftoxxx: error out when even/odd selects 0 pages

When page selection options and/or document length result in planned
output of a single page, further even/odd page selection can then
result in no pages being output.  Error out instead of producing no
output which is confusing to the user.

Closes: poppler/poppler#815
6 jobs for pdftoxxx_even_odd in 14 minutes and 10 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #1080160
build

00:14:10

passed #1080165
build_android

00:02:43

passed #1080161
build_clang_libcpp

00:12:56

passed #1080164
build_clazy

00:02:21

passed #1080163
build_mingw64_fedora

00:01:35

passed #1080162
build_ubuntu_16_04

00:01:30