fix: sonarExecuteScan: safeguard unstash of git metadata (#976)

* unstash .git folder only if not present, ignore missing stashes

* fix: negate condition

* Update sonarExecuteScan.groovy

vars/sonarExecuteScan.groovy

@@ -190,7 +190,9 @@ void call(Map parameters = [:]) {
             script: script,
             dockerImage: configuration.dockerImage
         ){
-            unstash 'git'
+            if(!script.fileExists('.git')) {
+                utils.unstash('git')
+            }
             worker(configuration)
         }
     }