[log] IDEA-125309 One more fix for a possible deadlock

General practice is not to invoke some external code under a lock.

Here the result handler can safely be called before the lock: if new
requests arrive, they will be added to the queue in request(), and a new
background task will be started after result is handled.

platform/vcs-log/impl/src/com/intellij/vcs/log/data/SingleTaskController.java

@@ -85,8 +85,8 @@ public abstract class SingleTaskController<Request, Result> {
    * The result is immediately passed to the result handler specified in the constructor.
    */
   protected final void taskCompleted(@NotNull Result result) {
+    myResultHandler.consume(result);
     synchronized (LOCK) {
-      myResultHandler.consume(result);
       if (myAwaitingRequests.isEmpty()) {
         myActive = false;
       }