fs: fix misplaced errors in fs.symlinkSync

The ctx.error is supposed to be handled in fs.readlinkSync,
but was handled in fs.symlinkSync by mistake.

Also fix the error number check in readlink to be consistent
with SYNC_CALL.

PR-URL: #18548
Refs: #18348
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

Author: joyeecheung

lib/fs.js

@@ -1161,6 +1161,11 @@ fs.readlinkSync = function(path, options) {
                                   options.encoding, undefined, ctx);
   if (ctx.errno !== undefined) {
     throw errors.uvException(ctx);
+  } else if (ctx.error) {
+    // TODO(joyeecheung): this is an encoding error usually caused by memory
+    // problems. We need to figure out proper error code(s) for this.
+    Error.captureStackTrace(ctx.error);
+    throw ctx.error;
   }
   return result;
 };
@@ -1232,11 +1237,6 @@ fs.symlinkSync = function(target, path, type) {
 
   if (ctx.errno !== undefined) {
     throw errors.uvException(ctx);
-  } else if (ctx.error) {
-    // TODO(joyeecheung): this is an encoding error usually caused by memory
-    // problems. We need to figure out proper error code(s) for this.
-    Error.captureStackTrace(ctx.error);
-    throw ctx.error;
   }
 };
 

src/node_file.cc

@@ -886,7 +886,7 @@ static void ReadLink(const FunctionCallbackInfo<Value>& args) {
     fs_req_wrap req;
     int err = SyncCall(env, args[3], &req, "readlink",
                        uv_fs_readlink, *path);
-    if (err) {
+    if (err < 0) {
       return;  // syscall failed, no need to continue, error info is in ctx
     }
     const char* link_path = static_cast<const char*>(req.req.ptr);