Fix a ref count mistake and add a long-overdue tf_util_print_backtrace() that helped me find it.

src/http.c

@@ -1019,7 +1019,7 @@ void tf_http_request_unref(tf_http_request_t* request)
 		tf_free(request);
 	}
 
-	if (--connection->ref_count == 0)
+	if (connection && --connection->ref_count == 0)
 	{
 		if (connection->http->is_shutting_down)
 		{

src/httpd.js.c

@@ -1541,7 +1541,6 @@ static void _httpd_endpoint_login_work(tf_ssb_t* ssb, void* user_data)
 	}
 	else
 	{
-		tf_http_request_ref(request);
 
 		login->name = account_name_copy;
 		login->error = login_error;
@@ -1566,6 +1565,7 @@ static void _httpd_endpoint_login_work(tf_ssb_t* ssb, void* user_data)
 		}
 
 		login->pending++;
+		tf_http_request_ref(request);
 		tf_file_read(login->request->user_data, "core/auth.html", _httpd_endpoint_login_file_read_callback, login);
 
 		account_name_copy = NULL;
@@ -1584,9 +1584,9 @@ done:
 static void _httpd_endpoint_login_after_work(tf_ssb_t* ssb, int status, void* user_data)
 {
 	login_request_t* login = user_data;
+	tf_http_request_t* request = login->request;
 	if (login->pending == 1)
 	{
-		tf_http_request_t* request = login->request;
 		if (*login->location_header)
 		{
 			const char* headers[] = {
@@ -1597,8 +1597,8 @@ static void _httpd_endpoint_login_after_work(tf_ssb_t* ssb, int status, void* us
 			};
 			tf_http_respond(request, 303, headers, tf_countof(headers) / 2, NULL, 0);
 		}
-		tf_http_request_unref(request);
 	}
+	tf_http_request_unref(request);
 	_login_release(login);
 }
 

src/util.js.c

@@ -435,6 +435,13 @@ const char* tf_util_backtrace_string()
 	return tf_util_backtrace_to_string(buffer, count);
 }
 
+void tf_util_print_backtrace()
+{
+	const char* bt = tf_util_backtrace_string();
+	tf_printf("%s\n", bt);
+	tf_free((void*)bt);
+}
+
 #if defined(__ANDROID__)
 typedef struct _android_backtrace_t
 {

src/util.js.h

@@ -126,6 +126,11 @@ const char* tf_util_backtrace_to_string(void* const* buffer, int count);
 */
 const char* tf_util_backtrace_string();
 
+/**
+** Print a stack backtrace of the calling thread.
+*/
+void tf_util_print_backtrace();
+
 /**
 ** Convert a function pointer to its name, if possible.
 ** @return The function name or null.