SplashXPathScanner: If any of the segments of the path is nan, path is not valid

Fixes crash in broken files #1022
7 jobs for 1022 in 7 minutes and 25 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #6444481
build

00:06:32

passed #6444486
build_android

00:01:01

passed #6444482
build_clang_libcpp

00:07:24

passed #6444485
build_clazy

00:02:31

passed #6444484
build_mingw64_fedora

00:03:09

passed #6444483
build_ubuntu_16_04

00:03:05

passed #6444480
clang_format

00:01:46