GUACAMOLE-2255: Fix intermittent rdp error handling due to uninitialized variable.

[bbennett-ks]

The connection_closing variable in rdp.c (line 627) is not initialized before use. When RDP event handling fails early in the do-while loop, the code breaks before connection_closing is assigned a value, leading to potentially aborting a RDP connection because of an error without report the closing as an error.    

This was caused by a fix for GUACAMOLE-2221 (fix RDP busy-loop on transport failure) which added a break.

I cam across this build Guacamole on Rocky 9.

{code:java}
rdp.c: In function 'guac_rdp_client_thread':
rdp.c:658:12: error: 'connection_closing' may be used uninitialized in this function [-Werror=maybe-uninitialized]
658 | if (connection_closing)
| ^
rdp.c:627:13: note: 'connection_closing' was declared here
627 | int connection_closing;
| ^~~~~~~~~~~~~~~~~~
{code}

[necouchman]

@bbennett-ks Can you remove the 2254 commit from this? Also, while commit messages are formatted correctly, the title of the PR is not... (Guacamole 2255).

[bbennett-ks]

@bbennett-ks Can you remove the 2254 commit from this? Also, while commit messages are formatted correctly, the title of the PR is not... (Guacamole 2255).

Thanks! Done.