Fixes two issues; the type error surfaced by use of strict_types in 2.3-develop and issue where SCD hangs ending in RuntimeException on 2.2-develop

Resolves #22563 and #21852

Author: davidalger

app/code/Magento/Deploy/Process/Queue.php

@@ -335,6 +335,11 @@ private function isDeployed(Package $package)
     {
         if ($this->isCanBeParalleled()) {
             if ($package->getState() === null) {
+                $pid = $this->getPid($package);
+                if ($pid === null) {
+                    return false;
+                }
+
                 // phpcs:ignore Magento2.Functions.DiscouragedFunction
                 $result = pcntl_waitpid($pid, $status, WNOHANG);
                 if ($result === $pid) {