Fix issues found by ineffassign

gocryptfs$ ineffassign ./...

/home/jakob/go/src/github.com/rfjakob/gocryptfs/internal/configfile/config_file.go:243:2: ineffectual assignment to scryptHash
/home/jakob/go/src/github.com/rfjakob/gocryptfs/internal/configfile/config_file.go:272:2: ineffectual assignment to scryptHash
/home/jakob/go/src/github.com/rfjakob/gocryptfs/internal/fusefrontend/file.go:285:3: ineffectual assignment to fileID
/home/jakob/go/src/github.com/rfjakob/gocryptfs/internal/fusefrontend/node.go:367:3: ineffectual assignment to err
/home/jakob/go/src/github.com/rfjakob/gocryptfs/internal/fusefrontend/node_open_create.go:68:2: ineffectual assignment to fd
/home/jakob/go/src/github.com/rfjakob/gocryptfs/mount.go:308:2: ineffectual assignment to masterkey
/home/jakob/go/src/github.com/rfjakob/gocryptfs/gocryptfs-xray/xray_main.go:156:13: ineffectual assignment to err
/home/jakob/go/src/github.com/rfjakob/gocryptfs/internal/fusefrontend/prepare_syscall_test.go:65:16: ineffectual assignment to errno
/home/jakob/go/src/github.com/rfjakob/gocryptfs/internal/syscallcompat/open_nofollow_test.go:34:2: ineffectual assignment to fd
/home/jakob/go/src/github.com/rfjakob/gocryptfs/tests/defaults/acl_test.go:111:6: ineffectual assignment to err
/home/jakob/go/src/github.com/rfjakob/gocryptfs/tests/defaults/acl_test.go:181:2: ineffectual assignment to sz
/home/jakob/go/src/github.com/rfjakob/gocryptfs/tests/defaults/acl_test.go:198:2: ineffectual assignment to sz
/home/jakob/go/src/github.com/rfjakob/gocryptfs/tests/defaults/main_test.go:365:8: ineffectual assignment to err
/home/jakob/go/src/github.com/rfjakob/gocryptfs/tests/xattr/xattr_fd_test.go:30:6: ineffectual assignment to err
/home/jakob/go/src/github.com/rfjakob/gocryptfs/tests/xattr/xattr_fd_test.go:66:6: ineffectual assignment to err

3 files changed, 12 insertions, 13 deletions

diff --git a/internal/fusefrontend/file.go b/internal/fusefrontend/file.go
index 716a0db..ef043ae 100644
--- a/internal/fusefrontend/file.go
+++ b/internal/fusefrontend/file.go
@@ -277,16 +277,13 @@ func (f *File) Read(ctx context.Context, buf []byte, off int64) (resultData fuse
 // Empty writes do nothing and are allowed.
 func (f *File) doWrite(data []byte, off int64) (uint32, syscall.Errno) {
 	fileWasEmpty := false
-	// Get the file ID, create a new one if it does not exist yet.
-	var fileID []byte
 	// The caller has exclusively locked ContentLock, which blocks all other
 	// readers and writers. No need to take IDLock.
-	if f.fileTableEntry.ID != nil {
-		fileID = f.fileTableEntry.ID
-	} else {
-		// If the file ID is not cached, read it from disk
+	//
+	// If the file ID is not cached, read it from disk
+	if f.fileTableEntry.ID == nil {
 		var err error
-		fileID, err = f.readFileID()
+		fileID, err := f.readFileID()
 		// Write a new file header if the file is empty
 		if err == io.EOF {
 			fileID, err = f.createHeader()
diff --git a/internal/fusefrontend/node.go b/internal/fusefrontend/node.go
index 8a3cfa2..7280624 100644
--- a/internal/fusefrontend/node.go
+++ b/internal/fusefrontend/node.go
@@ -354,23 +354,25 @@ func (n *Node) Symlink(ctx context.Context, target, name string, out *fuse.Entry
 	if !rn.args.PlaintextNames && nametransform.IsLongContent(cName) {
 		err = rn.nameTransform.WriteLongNameAt(dirfd, cName, name)
 		if err != nil {
-			errno = fs.ToErrno(err)
-			return
+			return nil, fs.ToErrno(err)
 		}
 		// Create "gocryptfs.longfile." symlink
 		err = syscallcompat.SymlinkatUser(cTarget, dirfd, cName, ctx2)
 		if err != nil {
 			nametransform.DeleteLongNameAt(dirfd, cName)
+			return nil, fs.ToErrno(err)
 		}
 	} else {
 		// Create symlink
 		err = syscallcompat.SymlinkatUser(cTarget, dirfd, cName, ctx2)
+		if err != nil {
+			return nil, fs.ToErrno(err)
+		}
 	}
 
 	st, err := syscallcompat.Fstatat2(dirfd, cName, unix.AT_SYMLINK_NOFOLLOW)
 	if err != nil {
-		errno = fs.ToErrno(err)
-		return
+		return nil, fs.ToErrno(err)
 	}
 	// Report the plaintext size, not the encrypted blob size
 	st.Size = int64(len(target))
diff --git a/internal/fusefrontend/prepare_syscall_test.go b/internal/fusefrontend/prepare_syscall_test.go
index 28e655c..693f62a 100644
--- a/internal/fusefrontend/prepare_syscall_test.go
+++ b/internal/fusefrontend/prepare_syscall_test.go
@@ -63,8 +63,8 @@ func TestPrepareAtSyscall(t *testing.T) {
 	syscall.Close(dirfd)
 
 	dirfd, cName, errno = rn.prepareAtSyscall("dir1")
-	if err != nil {
-		t.Fatal(err)
+	if errno != 0 {
+		t.Fatal(errno)
 	}
 	if cName == "" {
 		t.Fatal("cName should not be empty")