USB: only clear pending interrupts explicitely

Author: facchinm

cores/arduino/USB/SAMD21_USBDevice.h

@@ -394,8 +394,8 @@ class DoubleBufferedEPOutHandler : public EPHandler {
 					}
 				}
 			}
+			usbd.epAckPendingInterrupts(ep);
 		}
-		usbd.epAckPendingInterrupts(ep);
 	}
 
 	// Returns how many bytes are stored in the buffers

cores/arduino/USB/USBCore.cpp

@@ -909,9 +909,9 @@ void USBDeviceClass::ISRHandler()
 			} else {
 				#if defined(PLUGGABLE_USB_ENABLED)
 				PluggableUSB().handleEndpoint(ep);
+				usbd.epAckPendingInterrupts(ep);
 				#endif
 			}
-			usbd.epAckPendingInterrupts(ep);
 		}
 	}
 }