freenect: avoid leaking the context when fnusb_init() fails

Maybe this is more a theoretical issue than an actual one, I am not sure
in which case fnusb_init() —and hence libusb_init()— is supposed to
fail, but let's handle that once I noticed it.

Signed-off-by: Antonio Ospite <ospite@studenti.unina.it>

Author: Antonio Ospite

src/core.c

@@ -40,6 +40,8 @@
 
 FREENECTAPI int freenect_init(freenect_context **ctx, freenect_usb_context *usb_ctx)
 {
+	int res;
+
 	*ctx = (freenect_context*)malloc(sizeof(freenect_context));
 	if (!ctx)
 		return -1;
@@ -52,7 +54,12 @@ FREENECTAPI int freenect_init(freenect_context **ctx, freenect_usb_context *usb_
 			| FREENECT_DEVICE_AUDIO
 #endif
 			);
-	return fnusb_init(&(*ctx)->usb, usb_ctx);
+	res = fnusb_init(&(*ctx)->usb, usb_ctx);
+	if (res < 0) {
+		free(*ctx);
+		*ctx = NULL;
+	}
+	return res;
 }
 
 FREENECTAPI int freenect_shutdown(freenect_context *ctx)