fs: remove redundant code in readableWebStream()

Remove redundant code by moving it to outside of `if/else`. Plus,
make `options` optional in doc.

PR-URL: nodejs#49298
Reviewed-By: Debadree Chatterjee <debadree333@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

doc/api/fs.md

@@ -446,7 +446,7 @@ Reads data from the file and stores that in the given buffer.
 If the file is not modified concurrently, the end-of-file is reached when the
 number of bytes read is zero.
 
-#### `filehandle.readableWebStream(options)`
+#### `filehandle.readableWebStream([options])`
 
 <!-- YAML
 added: v17.0.0

lib/internal/fs/promises.js

@@ -282,17 +282,8 @@ class FileHandle extends EventEmitter {
         this[kHandle],
         undefined,
         { ondone: () => this[kUnref]() });
-
-      const {
-        readableStreamCancel,
-      } = require('internal/webstreams/readablestream');
-      this[kRef]();
-      this.once('close', () => {
-        readableStreamCancel(readable);
-      });
     } else {
       const {
-        readableStreamCancel,
         ReadableStream,
       } = require('internal/webstreams/readablestream');
 
@@ -319,14 +310,16 @@ class FileHandle extends EventEmitter {
           ondone();
         },
       });
-
-      this[kRef]();
-
-      this.once('close', () => {
-        readableStreamCancel(readable);
-      });
     }
 
+    const {
+      readableStreamCancel,
+    } = require('internal/webstreams/readablestream');
+    this[kRef]();
+    this.once('close', () => {
+      readableStreamCancel(readable);
+    });
+
     return readable;
   }