NormalAttrib: default props to 0 instead of undefined

9 jobs for normalattrib-initialize-0 in 4 minutes and 25 seconds
Status Job ID Name Coverage
  Test
passed #75654
VS2015
VS2015-32-bit

00:01:16

passed #75653
VS2015
VS2015-64-bit

00:01:23

passed #75652
VS2017
VS2017-32-bit

00:01:08

passed #75651
VS2015
VS2017-64-bit

00:01:29

passed #75648
Linux
clang-c++11

00:04:10

passed #75650
Linux
cppcheck

00:04:25

passed #75655
Linux
doc

00:00:19

passed #75647
Linux
gcc-c++11

00:02:57

passed #75649
Apple
macos-c++11

00:01:37