Halt _until_ data is available; do it only once.

Machines/Tandy/CoCo/DiskController.cpp

@@ -61,8 +61,10 @@ const Storage::Disk::Disk *DiskController::disk(const std::string &name) {
 //	* DRQ informs HALT, if enabled.
 //
 
-bool DiskController::halt() const {
-	return get_data_request_line() && enable_halt_;
+bool DiskController::halt() {
+	const bool halt = !get_data_request_line() && enable_halt_;
+	if(halt) enable_halt_ = false;
+	return halt;
 }
 
 bool DiskController::nmi() const {

Machines/Tandy/CoCo/DiskController.hpp

@@ -43,7 +43,7 @@ public:
 	void set_disk(std::shared_ptr<Storage::Disk::Disk>, size_t drive);
 	const Storage::Disk::Disk *disk(const std::string &);
 
-	bool halt() const;
+	bool halt();
 	bool nmi() const;
 
 private: