stock/BasicStock: move code from GetCreate() to GetCanceled()

GetCanceled() can be called even if the stock is full.

src/stock/BasicStock.cxx

@@ -246,18 +246,25 @@ BasicStock::GetIdle(StockRequest &request,
 	return true;
 }
 
-void
-BasicStock::GetCreate(StockRequest request,
-		      StockGetHandler &get_handler,
-		      CancellablePointer &cancel_ptr) noexcept
+bool
+BasicStock::GetCanceled(StockGetHandler &get_handler,
+			CancellablePointer &cancel_ptr) noexcept
 {
 	for (auto &c : create) {
 		if (c.IsDetached()) {
 			c.Attach(get_handler, cancel_ptr);
-			return;
+			return true;
 		}
 	}
 
+	return false;
+}
+
+void
+BasicStock::GetCreate(StockRequest request,
+		      StockGetHandler &get_handler,
+		      CancellablePointer &cancel_ptr) noexcept
+{
 	auto *c = new Create(*this,
 			     cls.ShouldContinueOnCancel(request.get()),
 			     get_handler, cancel_ptr);

src/stock/BasicStock.hxx

@@ -205,6 +205,15 @@ public:
 	bool GetIdle(StockRequest &request,
 		     StockGetHandler &handler) noexcept;
 
+	/**
+	 * Attach the handler to a canceled create request.
+	 *
+	 * @return true on success, false if no canceled create
+	 * requests exists
+	 */
+	bool GetCanceled(StockGetHandler &get_handler,
+			 CancellablePointer &cancel_ptr) noexcept;
+
 	void GetCreate(StockRequest request,
 		       StockGetHandler &get_handler,
 		       CancellablePointer &cancel_ptr) noexcept;

src/stock/Stock.cxx

@@ -118,9 +118,11 @@ Stock::RetryWaiting() noexcept
 	     --i) {
 		auto &w = waiting.pop_front();
 
-		GetCreate(std::move(w.request),
-			  w.handler,
-			  w.cancel_ptr);
+		if (!GetCanceled(w.handler, w.cancel_ptr))
+			GetCreate(std::move(w.request),
+				  w.handler,
+				  w.cancel_ptr);
+
 		w.Destroy();
 	}
 }
@@ -157,7 +159,8 @@ Stock::Get(StockRequest request,
 {
 	may_clear = false;
 
-	if (GetIdle(request, get_handler))
+	if (GetIdle(request, get_handler) ||
+	    GetCanceled(get_handler, cancel_ptr))
 		return;
 
 	if (IsFull()) {