Fix lower bounds checking for option keys.

Specifying an indexed option with a key of 0, e.g. pg0-path, would lead to a segfault.

Add lower bounds checking to fix the issue.

doc/xml/release/2025/2.56.0.xml

@@ -1,2 +1,19 @@
 <release date="XXXX-XX-XX" version="2.56.0dev" title="UNDER DEVELOPMENT">
+    <release-core-list>
+        <release-bug-list>
+            <release-item>
+                <github-issue id="2610"/>
+                <github-pull-request id="2611"/>
+
+                <release-item-contributor-list>
+                    <release-item-ideator id="wolfgang.walther"/>
+                    <release-item-contributor id="david.steele"/>
+                    <release-item-reviewer id="david.christensen"/>
+                    <release-item-reviewer id="wolfgang.walther"/>
+                </release-item-contributor-list>
+
+                <p>Fix lower bounds checking for option keys.</p>
+            </release-item>
+        </release-bug-list>
+    </release-core-list>
 </release>

doc/xml/release/contributor.xml

@@ -1181,6 +1181,11 @@
     <contributor-id type="github">mydimension</contributor-id>
 </contributor>
 
+<contributor id="wolfgang.walther">
+    <contributor-name-display>Wolfgang Walther</contributor-name-display>
+    <contributor-id type="github">wolfgangwalther</contributor-id>
+</contributor>
+
 <contributor id="wu.ning">
     <contributor-name-display>Wu Ning</contributor-name-display>
     <contributor-id type="github">50wu</contributor-id>