Apply suggestions from code review

Author: MichaelSimons

eng/common/templates-official/steps/source-build.yml

@@ -131,5 +131,5 @@ steps:
   inputs:
     ${{ if eq(length(parameters.cgIgnoreDirectories), 0) }}:
       ignoreDirectories: '$(Build.SourcesDirectory)/artifacts/source-build/self/src/artifacts/obj/source-built-upstream-cache'
-    ${{ if gt(length(parameters.cgIgnoreDirectories), 0) }}:
+    ${{ else }}:
       ignoreDirectories: ${{ join(',', parameters.cgIgnoreDirectories) }}

eng/common/templates/steps/source-build.yml

@@ -131,5 +131,5 @@ steps:
   inputs:
     ${{ if eq(length(parameters.cgIgnoreDirectories), 0) }}:
       ignoreDirectories: '$(Build.SourcesDirectory)/artifacts/source-build/self/src/artifacts/obj/source-built-upstream-cache'
-    ${{ if gt(length(parameters.cgIgnoreDirectories), 0) }}:
+    ${{ else }}:
       ignoreDirectories: ${{ join(',', parameters.cgIgnoreDirectories) }}