Slightly improve guards.

Changelog excerpt:
- Slightly improved guards for the IPHeader class trySource method.

Changelog.txt

@@ -11,7 +11,8 @@ found at:
 
 === Changes made since last versioned release ===
 
-(none)
+- [2024.03.21; Maikuolan]: Slightly improved guards for the IPHeader class
+  trySource method.
 
 === Version/Release 2.12.0 ===
 MINOR RELEASE.

src/IPHeader.php

@@ -1,6 +1,6 @@
 <?php
 /**
- * IP header class (last modified: 2023.09.14).
+ * IP header class (last modified: 2024.03.21).
  *
  * This file is a part of the "common classes package", utilised by a number of
  * packages and projects, including CIDRAM and phpMussel.
@@ -116,7 +116,7 @@ public function isValidIpv6(string $IP): bool
     public function trySource(string $Source): string
     {
         /** Fail immediately if the source isn't available. */
-        if (!isset($_SERVER[$Source]) || strlen($_SERVER[$Source]) === 0) {
+        if (!isset($_SERVER[$Source]) || !is_string($_SERVER[$Source]) || strlen($_SERVER[$Source]) === 0) {
             return '';
         }
 
@@ -126,6 +126,9 @@ public function trySource(string $Source): string
         /** Ensure that we're working with a string. */
         if (is_array($Try)) {
             $Try = array_shift($Try);
+            if (!is_string($Try)) {
+                return '';
+            }
         }
 
         /**