Address PR comments

scripts/build/Jenkins/Jenkinsfile

@@ -18,7 +18,7 @@ EMPTY_JSON = readJSON text: '{}'
 
 ENGINE_REPOSITORY_NAME = 'o3de'
 
-BUILD_SNAPSHOTS = ['development', 'stabilization/2106']
+BUILD_SNAPSHOTS = ['development', 'stabilization/2106', '']
 DEFAULT_BUILD_SNAPSHOT = BUILD_SNAPSHOTS.get(0)
 
 def pipelineProperties = []
@@ -458,10 +458,10 @@ try {
                         branchName = env.BRANCH_NAME
                     } else {
                         branchName = scm.branches[0].name // for non-multibranch pipelines
-                        env.BRANCH_NAME = branchName // so scripts that read this environment have it (e.g. incremental_build_util.py)
-                        choice(defaultValue: DEFAULT_BUILD_SNAPSHOT, name: 'SNAPSHOT', choices: BUILD_SNAPSHOTS, description: 'Selects the build snapshot to use. A more diverted snapshot will cause longer build times, but will not cause build failures.')
+                        env.BRANCH_NAME = branchName // so scripts that read this environment have it (e.g. incremental_build_util.py)                        
                     }
                     if(env.CHANGE_TARGET) {
+                        // PR builds
                         if(BUILD_SNAPSHOTS.contains(env.CHANGE_TARGET)) {
                             snapshot = env.CHANGE_TARGET
                             echo "Snapshot for destination branch \"${env.CHANGE_TARGET}\" found."
@@ -470,6 +470,8 @@ try {
                             echo "Snapshot for destination branch \"${env.CHANGE_TARGET}\" does not exist, defaulting to snapshot \"${snapshot}\""
                         }
                     } else {
+                        // Non-PR builds
+                        choice(defaultValue: DEFAULT_BUILD_SNAPSHOT, name: 'SNAPSHOT', choices: BUILD_SNAPSHOTS, description: 'Selects the build snapshot to use. A more diverted snapshot will cause longer build times, but will not cause build failures.')
                         snapshot = env.SNAPSHOT
                         echo "Snapshot \"${snapshot}\" selected."
                     }