IOS7: Trigger joystick presses only once for buttons A and B

All buttons and triggers on MFi game controllers are pressure sensitive
which means that when pressing buttons the registered
valueChangedHandler function is called multiple times providing updates
on the pressure value the button is pressed with. This causes multiple
kInputJoystickButtonDown events to be sent to the EventManager.
In adventure games the pressure value is not relevant and could cause
problems for the user that it triggers multiple presses on e.g. the B
button which often is mapped to the right mouse button. In some games
a click on the right mouse button changes what action that should be
performed.

Keep track on if the joystick buttons A or B (often mapped as left and
right mouse buttons) are being pressed. If the button is already
pressed do not add a new event until the button isn't pressed anymore.

To not interfere with any open dialog, don't send key events while the
keyboard is visible.

backends/platform/ios7/ios7_game_controller.mm

@@ -117,7 +117,30 @@
 }
 
 - (void)handleJoystickButtonAction:(int)button isPressed:(bool)pressed {
-	[view addEvent:InternalEvent(pressed ? kInputJoystickButtonDown : kInputJoystickButtonUp, button, 0)];
+	bool addEvent = true;
+	if (button == Common::JOYSTICK_BUTTON_A) {
+		if (_firstButtonPressed) {
+			if (pressed) {
+				addEvent = false;
+			}
+		}
+		_firstButtonPressed = pressed;
+	} else if (button == Common::JOYSTICK_BUTTON_B) {
+		if (_secondButtonPressed) {
+			if (pressed) {
+				addEvent = false;
+			}
+		}
+		_secondButtonPressed = pressed;
+	}
+	// Do not send button presses if keyboard is shown because if e.g.
+	// the "Do you want to quit?" dialog is shown the wait for user
+	// input will end (treating the button push as a mouse click) while
+	// the user tried to select the "y" or "n" character on the tvOS
+	// keyboard.
+	if (addEvent && ![view isKeyboardShown]) {
+		[view addEvent:InternalEvent(pressed ? kInputJoystickButtonDown : kInputJoystickButtonUp, button, 0)];
+	}
 }
 
 @end