darwin: handle error from GetConfigurationDescriptorPtr

When a device is disconnected or otherwise `dpriv->device` is invalid,
`GetConfigurationDescriptorPtr` will return `kIOReturnNoDevice` and
`IOUSBConfigurationDescriptorPtr` will not be set. This means that we
have an uninitialized pointer that is read from which is... very bad.

Author: osy

libusb/os/darwin_usb.c

@@ -698,9 +698,9 @@ static int get_configuration_index (struct libusb_device *dev, UInt8 config_valu
     return darwin_to_libusb (kresult);
 
   for (i = 0 ; i < numConfig ; i++) {
-    (*(priv->device))->GetConfigurationDescriptorPtr (priv->device, i, &desc);
+    kresult = (*(priv->device))->GetConfigurationDescriptorPtr (priv->device, i, &desc);
 
-    if (desc->bConfigurationValue == config_value)
+    if (kresult == kIOReturnSuccess && desc->bConfigurationValue == config_value)
       return i;
   }
 
@@ -1823,7 +1823,10 @@ static int darwin_reenumerate_device (struct libusb_device_handle *dev_handle, b
   cached_configurations = alloca (sizeof (*cached_configurations) * descriptor.bNumConfigurations);
 
   for (i = 0 ; i < descriptor.bNumConfigurations ; ++i) {
-    (*(dpriv->device))->GetConfigurationDescriptorPtr (dpriv->device, i, &cached_configuration);
+    kresult = (*(dpriv->device))->GetConfigurationDescriptorPtr (dpriv->device, i, &cached_configuration);
+    if (kresult != kIOReturnSuccess) {
+      return LIBUSB_ERROR_NOT_FOUND;
+    }
     memcpy (cached_configurations + i, cached_configuration, sizeof (cached_configurations[i]));
   }
 
@@ -1883,8 +1886,8 @@ static int darwin_reenumerate_device (struct libusb_device_handle *dev_handle, b
   }
 
   for (i = 0 ; i < descriptor.bNumConfigurations ; ++i) {
-    (void) (*(dpriv->device))->GetConfigurationDescriptorPtr (dpriv->device, i, &cached_configuration);
-    if (memcmp (cached_configuration, cached_configurations + i, sizeof (cached_configurations[i]))) {
+    kresult = (*(dpriv->device))->GetConfigurationDescriptorPtr (dpriv->device, i, &cached_configuration);
+    if (kresult != kIOReturnSuccess || memcmp (cached_configuration, cached_configurations + i, sizeof (cached_configurations[i]))) {
       usbi_dbg (ctx, "darwin/reenumerate_device: configuration descriptor %d changed", i);
       return LIBUSB_ERROR_NOT_FOUND;
     }