Work CD-CI

- Improve PR check.

***NO_CI***

azure-pipelines.yml

@@ -55,7 +55,7 @@ jobs:
     # get commit message
   - powershell: |
 
-      if($env:Build_Reason -eq 'PullRequest')
+      if($env:System_PullRequest_PullRequestId -ne $null)
       {
         # PR build, get PR message
 
@@ -100,7 +100,7 @@ jobs:
 
   - powershell: |
 
-      if($env:Build_Reason -eq 'PullRequest')
+      if($env:System_PullRequest_PullRequestId -ne $null)
       {
         # this is a PR: always build depending on target tag
         echo "##vso[task.setvariable variable=GO;isOutput=true]False"