net_helper: do not propagate exceptions through dtor

Coverity 161864

contrib/epee/include/net/net_helper.h

@@ -106,7 +106,8 @@ namespace net_utils
 			~blocked_mode_client()
 		{
 			//profile_tools::local_coast lc("~blocked_mode_client()", 3);
-			shutdown();
+			try { shutdown(); }
+			catch(...) { /* ignore */ }
 		}
 
     inline