Fixes test flakiness by forcing the test client to reconnect after fuzzed requests.

$ blaze test //gfe/gfe2/e2e:fuzz_internal_urls_test_autobahn_tcp_with_autobahn_tcp_backends --runs_per_test=1000 --test_arg=--gfe2_reloadable_flag_autobahn_boost_tokens_sooner=true

//gfe/gfe2/e2e:fuzz_internal_urls_test_autobahn_tcp_with_autobahn_tcp_backends PASSED in 101.0s
  Stats over 1000 runs: max = 101.0s, min = 26.4s, avg = 46.0s, dev = 11.4s

http://sponge2/45f3aa80-7887-4343-8b71-982b4daebac9

PiperOrigin-RevId: 351894605
Change-Id: I4538f1a7031bab7ace1db5cc77301c69fdf0d6b3

quic/test_tools/quic_test_client.cc

diff --git a/quic/test_tools/quic_test_client.cc b/quic/test_tools/quic_test_client.cc
index eaec7eb..9dcfb42 100644
--- a/quic/test_tools/quic_test_client.cc
+++ b/quic/test_tools/quic_test_client.cc
@@ -658,7 +658,9 @@
 
 void QuicTestClient::Disconnect() {
   ClearPerConnectionState();
-  client_->Disconnect();
+  if (client_->initialized()) {
+    client_->Disconnect();
+  }
   connect_attempted_ = false;
 }