docs: fix simple-profiling.md (#3988)

Fix missing negation before users[username] to check if there is no user with the inserted username. This aligns the code snippet with the one that below which implements the same check.

Author: 1110sillabo

locale/en/docs/guides/simple-profiling.md

@@ -37,7 +37,7 @@ app.get('/newUser', (req, res) => {
 
   username = username.replace(/[!@#$%^&*]/g, '');
 
-  if (!username || !password || users[username]) {
+  if (!username || !password || !users[username]) {
     return res.sendStatus(400);
   }
 

locale/es/docs/guides/simple-profiling.md

@@ -26,7 +26,7 @@ app.get('/newUser', (req, res) => {
 
   username = username.replace(/[!@#$%^&*]/g, '');
 
-  if (!username || !password || users[username]) {
+  if (!username || !password || !users[username]) {
     return res.sendStatus(400);
   }
 

locale/ko/docs/guides/simple-profiling.md

@@ -64,7 +64,7 @@ app.get('/newUser', (req, res) => {
 
   username = username.replace(/[!@#$%^&*]/g, '');
 
-  if (!username || !password || users.username) {
+  if (!username || !password || !users[username]) {
     return res.sendStatus(400);
   }
 
@@ -87,7 +87,7 @@ app.get('/newUser', (req, res) => {
 
   username = username.replace(/[!@#$%^&*]/g, '');
 
-  if (!username || !password || users.username) {
+  if (!username || !password || !users[username]) {
     return res.sendStatus(400);
   }
 

locale/ro/docs/guides/simple-profiling.md

@@ -26,7 +26,7 @@ app.get('/newUser', (req, res) => {
 
   username = username.replace(/[!@#$%^&*]/g, '');
 
-  if (!username || !password || users[username]) {
+  if (!username || !password || !users[username]) {
     return res.sendStatus(400);
   }
 

locale/ru/docs/guides/simple-profiling.md

@@ -36,7 +36,7 @@ app.get('/newUser', (req, res) => {
 
   username = username.replace(/[!@#$%^&*]/g, '');
 
-  if (!username || !password || users[username]) {
+  if (!username || !password || !users[username]) {
     return res.sendStatus(400);
   }
 

locale/zh-cn/docs/guides/simple-profiling.md

@@ -26,7 +26,7 @@ app.get('/newUser', (req, res) => {
 
   username = username.replace(/[!@#$%^&*]/g, '');
 
-  if (!username || !password || users.username) {
+  if (!username || !password || !users.username) {
     return res.sendStatus(400);
   }