Addressing some PHP8 incompatibilities - Diffusion & Differential

Summary: Running through setting up and using Diffusion repositories and addressing PHP8 issues that come up.

Test Plan:
I set up a hosted mercurial repository and pushed commits to it over ssh.
I set up a hosted git repository and pushed commits to it over ssh.
I set up a mirrored mercurial repository over ssh.
I set up a mirrored git repository over ssh.

I created a diff on a git repository and landed it.
I created a diff on a mercurial repository and landed it.

I cloned and pushed a commit to a mercurial repo over http.
I cloned and pushed a commit to a git repo over http.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D21864

Author: neandrake

scripts/ssh/ssh-auth.php

@@ -36,7 +36,7 @@
 
 $authstruct = null;
 
-if (strlen($authstruct_raw)) {
+if ($authstruct_raw !== null && strlen($authstruct_raw)) {
   try {
     $authstruct = phutil_json_decode($authstruct_raw);
   } catch (Exception $ex) {
@@ -135,7 +135,7 @@
 
   $cmd = csprintf('%s %Ls', $bin, $key_argv);
 
-  if (strlen($instance)) {
+  if ($instance !== null && strlen($instance)) {
     $cmd = csprintf('PHABRICATOR_INSTANCE=%s %C', $instance, $cmd);
   }
 

src/applications/almanac/util/AlmanacKeys.php

@@ -58,7 +58,7 @@ public static function getLiveDevice() {
 
   public static function getClusterSSHUser() {
     $username = PhabricatorEnv::getEnvConfig('diffusion.ssh-user');
-    if (strlen($username)) {
+    if ($username !== null && strlen($username)) {
       return $username;
     }