Fix for conductivity in items with null second material. Issue #6190
Merge branch 'master' into conductivityfix
Merge branch 'master' of https://github.com/CleverRaven/Cataclysm-DDA into conductivityfix

Merge conductivity fix with upstream/master
Merge branch 'master' of https://github.com/CleverRaven/Cataclysm-DDA into conductivityfix
Keep fix in tune with upstream/master

Need to switch to diff branch
Merge branch 'master' of https://github.com/CleverRaven/Cataclysm-DDA into conductivityfix
keep in step with upstream master
Slightly different method of fixing conductivity issue #6190
Merge branch 'master' of https://github.com/CleverRaven/Cataclysm-DDA into conductivityfix
:
Merge branch 'conductivityfix' of https://github.com/frycarson/Cataclysm-DDA into frycarson-conductivityfix