Fix mosquitto_passwd -b not updating passwords for existing users

Closes eclipse#1664. Thanks to Leon Kiefer.

ChangeLog.txt

@@ -1,6 +1,9 @@
 Broker:
 - Report invalid bridge prefix+pattern combinations at config parsing time
  rather than letting the bridge fail later. Issue #1635.
+- Fix `mosquitto_passwd -b` not updating passwords for existing users
+ correctly. Creating a new user with `-b` worked without problem.
+ Closes #1664.
 
 Client library:
 - Don't treat an unexpected PUBACK, PUBREL, or PUBCOMP as a fatal error.

src/mosquitto_passwd.c

@@ -337,7 +337,7 @@ static int update_pwuser_cb(FILE *fptr, FILE *ftmp, const char *username, const
  }else{
  /* Write out a new line for our matching username */
  helper->found = true;
- rc = output_new_password(ftmp, username, password);
+ rc = output_new_password(ftmp, username, helper->password);
  }
  return rc;
 }
@@ -349,6 +349,7 @@ int update_pwuser(FILE *fptr, FILE *ftmp, const char *username, const char *pass
 
  memset(&helper, 0, sizeof(helper));
  helper.username = username;
+ helper.password = password;
  rc = pwfile_iterate(fptr, ftmp, update_pwuser_cb, &helper);
 
  if(helper.found){