ANDROID: incremental-fs: fix GPF in pending_reads_dispatch_ioctl

It is possible that fget returns NULL. This needs to be handled
correctly in ioctl_permit_fill.

Bug: 212821226

Signed-off-by: Tadeusz Struk <tadeusz.struk@linaro.org>
Change-Id: Iec8be21982afeab6794b78ab1a542671c52acea2

fs/incfs/pseudo_files.c

@@ -147,8 +147,12 @@ static long ioctl_permit_fill(struct file *f, void __user *arg)
 		return -EFAULT;
 
 	file = fget(permit_fill.file_descriptor);
-	if (IS_ERR(file))
+	if (IS_ERR_OR_NULL(file)) {
+		if (!file)
+			return -ENOENT;
+
 		return PTR_ERR(file);
+	}
 
 	if (file->f_op != &incfs_file_ops) {
 		error = -EPERM;