fix: prevent possible null pointer issues

Author: mikesmitty

src/machine/usb.go

@@ -213,7 +213,10 @@ func handleStandardSetup(setup usb.Setup) bool {
 		if setup.WValueL == 1 { // DEVICEREMOTEWAKEUP
 			isRemoteWakeUpEnabled = false
 		} else if setup.WValueL == 0 { // ENDPOINTHALT
-			if usbStallHandler[setup.WIndex&0x7F] != nil {
+			if setup.WIndex < usb.NumberOfEndpoints && usbStallHandler[setup.WIndex&0x7F] != nil {
+				// Host has requested to clear an endpoint stall. If the request is addressed to
+				// an endpoint with a configured StallHandler, forward the message on.
+				// The 0x7F mask is used to clear the direction bit from the endpoint number
 				return usbStallHandler[setup.WIndex&0x7F](setup)
 			}
 			isEndpointHalt = false
@@ -225,7 +228,10 @@ func handleStandardSetup(setup usb.Setup) bool {
 		if setup.WValueL == 1 { // DEVICEREMOTEWAKEUP
 			isRemoteWakeUpEnabled = true
 		} else if setup.WValueL == 0 { // ENDPOINTHALT
-			if usbStallHandler[setup.WIndex&0x7F] != nil {
+			if setup.WIndex < usb.NumberOfEndpoints && usbStallHandler[setup.WIndex&0x7F] != nil {
+				// Host has requested to stall an endpoint. If the request is addressed to
+				// an endpoint with a configured StallHandler, forward the message on.
+				// The 0x7F mask is used to clear the direction bit from the endpoint number
 				return usbStallHandler[setup.WIndex&0x7F](setup)
 			}
 			isEndpointHalt = true