Blank SSH user and/or password need a prompt when connecting, not a message dialog

[b-fett]

Expected behavior

Connection to be established successfully.

Current behavior

Raising error window "Can't connect to MySQL server on 'localhost' (10061)"

Steps to reproduce

1. Create new connection with next settings:

• Network type: MySQL (SSH tunnel)

• Hostname / IP: localhost

• Prompt for credentials: checked

• SSH host + prot: my_host_IP

• Username: blank

• Password: blank

2. Open created connection
3. Type mysql credentials in according fields, hit Login
4. Type SSH user name while focus on authentification dialog
   
   and hit OK
5. Error window appears here.

Context

• HeidiSQL version: 9.5.0.5245
• Database system + version: Ubuntu 16.04.3 LTS, 10.2.12-MariaDB
• Operating system: Windows 7 (6.1.7601)

Failure Logs

Connecting to localhost via MariaDB (SSH tunnel), username root, using password: Yes ...
Attempt to create plink.exe process, waiting 4s for response ...
plink.exe -ssh my_host_IP -N -L 3307:localhost:3306
Can't connect to MySQL server on 'localhost' (10061)
Closing plink.exe process #2932 ...

[b-fett]

plink version is 0.68

[ansgarbecker]

Blank SSH user + passwords are currently not supported by HeidiSQL, as this requires a prompting approach in the upcoming dialog.