Fix potential deadlock when PageBufferClient exceeds memory limit

Prior to this change, if the PageBufferClient caused a task to exceed
its memory limit inside of addPages, the exception would bubble to the
root of the exchange client callback executor without ever marking the
task as failed. If no other operator also saw the memory limit
exceeded condition, then the task would become stuck in a deadlocked
state.

presto-main/src/main/java/com/facebook/presto/operator/PageBufferClient.java

@@ -309,26 +309,26 @@ public void onSuccess(PagesResponse result)
                         // This is to fast release the pages on the buffer side.
                         resultClient.acknowledgeResultsAsync(result.getNextToken());
                     }
+
+                    // add pages:
+                    // addPages must be called regardless of whether pages is an empty list because
+                    // clientCallback can keep stats of requests and responses. For example, it may
+                    // keep track of how often a client returns empty response and adjust request
+                    // frequency or buffer size.
+                    if (clientCallback.addPages(PageBufferClient.this, pages)) {
+                        pagesReceived.addAndGet(pages.size());
+                        rowsReceived.addAndGet(pages.stream().mapToLong(SerializedPage::getPositionCount).sum());
+                    }
+                    else {
+                        pagesRejected.addAndGet(pages.size());
+                        rowsRejected.addAndGet(pages.stream().mapToLong(SerializedPage::getPositionCount).sum());
+                    }
                 }
                 catch (PrestoException e) {
                     handleFailure(e, resultFuture);
                     return;
                 }
 
-                // add pages:
-                // addPages must be called regardless of whether pages is an empty list because
-                // clientCallback can keep stats of requests and responses. For example, it may
-                // keep track of how often a client returns empty response and adjust request
-                // frequency or buffer size.
-                if (clientCallback.addPages(PageBufferClient.this, pages)) {
-                    pagesReceived.addAndGet(pages.size());
-                    rowsReceived.addAndGet(pages.stream().mapToLong(SerializedPage::getPositionCount).sum());
-                }
-                else {
-                    pagesRejected.addAndGet(pages.size());
-                    rowsRejected.addAndGet(pages.stream().mapToLong(SerializedPage::getPositionCount).sum());
-                }
-
                 synchronized (PageBufferClient.this) {
                     // client is complete, acknowledge it by sending it a delete in the next request
                     if (result.isClientComplete()) {