fix crash in polylinecollection, when no edge_scalars are present

7 jobs for polylinecollection in 64 minutes and 8 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #17793
Apple
Mac-Cpp11

01:04:08

passed #17792
Qt551 VS2013
VS2013-Qt-5.5.1-x64

00:15:02

passed #17791
Qt56 VS2015
VS2015-Qt-5.6.0-x32

00:19:52

passed #17790
Qt56 VS2015
VS2015-Qt-5.6.0-x64

00:17:24

passed #17788
MultiThreads Linux
clang-c++11-Qt5

00:08:32

passed #17789
MultiThreads Linux
cppcheck

00:38:49

passed #17787
Linux
gcc-c++11-Qt5

00:03:40