PR 56873 make sure connection is established when reading last modified

WHATSNEW

@@ -27,6 +27,11 @@ Fixed bugs:
    cannot determine the local hostname.
    Bugzilla Report 56593
 
+ * URLResource#getLastModified tried to access the connection to the
+   URL without making sure it was established, potentially leading to
+   a NullPointerException.
+   Bugzilla Report 56873
+
 Other changes:
 --------------
 

src/main/org/apache/tools/ant/types/resources/URLResource.java

@@ -265,7 +265,14 @@ public class URLResource extends Resource implements URLProvider {
         if (!isExists(false)) {
             return 0L;
         }
-        return conn.getLastModified();
+        try {
+            connect();
+            long lastModified = conn.getLastModified();
+            close();
+            return lastModified;
+        } catch (IOException e) {
+            return UNKNOWN_DATETIME;
+        }
     }
 
     /**