Don't decrement mising projects

Author: tvernum

x-pack/plugin/security/src/main/java/org/elasticsearch/xpack/security/support/SecurityMigrations.java

@@ -372,7 +372,10 @@ private void incrementAttemptCount(ProjectId project) {
         }
 
         private void decrementAttemptCount(ProjectId project) {
-            taskSubmissionAttemptCounter.computeIfAbsent(project, ignore -> new AtomicInteger(0)).decrementAndGet();
+            final AtomicInteger counter = taskSubmissionAttemptCounter.get(project);
+            if (counter != null) {
+                counter.decrementAndGet();
+            }
         }
 
     }