Wrap call to LafManager.getInstance().getCurrentUIThemeLookAndFeel() in null check to prevent NPE during headless testing.

[ChrisCarini]

Summary

Wrap call to LafManager.getInstance().getCurrentUIThemeLookAndFeel() in null check to prevent NPE during headless testing.

Issue

See below for details:

• https://intellij-support.jetbrains.com/hc/en-us/community/posts/16040325332882-Calling-AboutTroubleInfoCollector-collectInfo-method-throws-NPE-in-tests-because-of-com-intellij-ide-ui-LafManager-getCurrentUIThemeLookAndFeel-is-null?page=1#community_comment_16830339751954
• https://youtrack.jetbrains.com/issue/IDEA-345108/Calling-AboutTroubleInfoCollector.collectInfo-method-throws-NPE-in-tests-because-of