tls,http2: handle writes after SSL destroy more gracefully

This might otherwise result in a hard crash when trying
to write to a socket after a sudden disconnect.

Note that the test here uses an aborted `h2load` run to create
the failing requests; That’s far from ideal, but it provides
a reasonably reliably reproduction at this point.

Backport-PR-URL: #22924
PR-URL: #18987
Fixes: #18973
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Matteo Collina <[email protected]>

Author: addaleax

src/tls_wrap.cc

@@ -601,7 +601,12 @@ int TLSWrap::DoWrite(WriteWrap* w,
                      size_t count,
                      uv_stream_t* send_handle) {
   CHECK_EQ(send_handle, nullptr);
-  CHECK_NE(ssl_, nullptr);
+
+  if (ssl_ == nullptr) {
+    ClearError();
+    error_ = "Write after DestroySSL";
+    return UV_EPROTO;
+  }
 
   bool empty = true;
 
@@ -642,12 +647,6 @@ int TLSWrap::DoWrite(WriteWrap* w,
     return 0;
   }
 
-  if (ssl_ == nullptr) {
-    ClearError();
-    error_ = "Write after DestroySSL";
-    return UV_EPROTO;
-  }
-
   crypto::MarkPopErrorOnReturn mark_pop_error_on_return;
 
   int written = 0;