revert e8b160a which didn't fix anything but rather broke stuff

WHATSNEW

@@ -27,11 +27,6 @@ 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

@@ -263,16 +263,10 @@ public class URLResource extends Resource implements URLProvider {
             return ((Resource) getCheckedRef()).getLastModified();
         }
         if (!isExists(false)) {
-            return 0L;
-        }
-        try {
-            connect();
-            long lastModified = conn.getLastModified();
-            close();
-            return lastModified;
-        } catch (IOException e) {
             return UNKNOWN_DATETIME;
         }
+        // isExists has already opened the connection
+        return conn.getLastModified();
     }
 
     /**