Bugfix SQLServerMemory semaphore not released properly (#883)

## Motivation and Context (Why the change? What's the scenario?)

A simple bugfix for SQLServerMemory. The semaphore wasn't released when
"is ready" changes from "false" to "true" while the code was waiting for
the semaphore. Meaning if specifically 3 or more tasks run into that
code at the same time, the third task as well as all others are gonna be
stuck in a deadlock waiting for the semaphore. This only happens during
the first initialization, since subsequent calls will leave before
waiting for the semaphore.

extensions/SQLServer/SQLServer/SqlServerMemory.cs

@@ -397,10 +397,11 @@ private async Task InitAsync(CancellationToken cancellationToken)
         if (this._isReady) { return; }
 
         await this._initSemaphore.WaitAsync(cancellationToken).ConfigureAwait(false);
-        if (this._isReady) { return; }
 
         try
         {
+            if (this._isReady) { return; }
+
             await this.CacheSqlServerMajorVersionNumberAsync(cancellationToken).ConfigureAwait(false);
             await this.CreateTablesIfNotExistsAsync(cancellationToken).ConfigureAwait(false);
             this._isReady = true;