added update user change user and change password

src/user.c

@@ -24,8 +24,8 @@ void free_request_with_token(request_with_token *data) {
   free(data);
 }
 
-User *new_user(int id, const char *username, const char *password, const char *email,
-               const char *group, bool is_superuser) {
+User *new_user(int id, const char *username, const char *password,
+               const char *email, const char *group, bool is_superuser) {
   User *user = malloc(sizeof(User));
   if (user == NULL) {
     return NULL;
@@ -40,9 +40,20 @@ User *new_user(int id, const char *username, const char *password, const char *e
 }
 
 void free_user(User *user) {
-  free(user->username);
-  free(user->password);
-  free(user->email);
-  free(user->group);
+  if (!user) {
+    return;
+  }
+  if (user->username != nullptr) {
+    free(user->username);
+  }
+  if (user->password != nullptr) {
+    free(user->password);
+  }
+  if (user->email != nullptr) {
+    free(user->email);
+  }
+  if (user->group != nullptr) {
+    free(user->group);
+  }
   free(user);
 }