added fixes to azure blob storage asset store

src/Squidex.Infrastructure.Azure/Storage/AzureBlobAssetStore.cs

@@ -65,7 +65,7 @@ namespace Squidex.Infrastructure.Azure.Storage
             var blob = blobContainer.GetBlockBlobReference(blobName);
 
             if (!await blob.ExistsAsync())
-                return;
+                throw new AssetNotFoundException($"Asset {blobName} not found.");
 
             await blob.DownloadToStreamAsync(stream);
         }
@@ -98,7 +98,10 @@ namespace Squidex.Infrastructure.Azure.Storage
         {
             try
             {
-                blobContainer = azureStorageAccount.GetContainer(containerName);
+                var task = azureStorageAccount.GetContainerAsync(containerName);
+                task.Wait();
+
+                blobContainer = task.Result;
             }
             catch (Exception)
             {

src/Squidex.Infrastructure.Azure/Storage/IStorageAccountManager.cs

@@ -17,6 +17,6 @@ namespace Squidex.Infrastructure.Azure.Storage
 
         string GetSharedAccessSignature();
 
-        CloudBlobContainer GetContainer(string name);
+        Task<CloudBlobContainer> GetContainerAsync(string name);
     }
 }

src/Squidex.Infrastructure.Azure/Storage/StorageAccountManager.cs

@@ -45,10 +45,13 @@ namespace Squidex.Infrastructure.Azure.Storage
             });
         }
 
-        public CloudBlobContainer GetContainer(string name)
+        public async Task<CloudBlobContainer> GetContainerAsync(string name)
         {
             var blobClient = CreateCloudBlobClient();
-            return blobClient.GetContainerReference(name);
+            var container = blobClient.GetContainerReference(name);
+            await container.CreateIfNotExistsAsync();
+
+            return container;
         }
     }
 }