Correction for passing zero-length SQL to trace (#8748)

* Pass SQL with zero length in trace correctly

* Add forgotten change

* Calculate size only when empty sql is encountered

* Use explicit way to update calculate SQL length

---------

Co-authored-by: Artyom Abakumov <artyom.abakumov@red-soft.ru>

Author: Noremos

src/jrd/trace/TraceDSQLHelpers.h

@@ -53,14 +53,14 @@ class TraceDSQLPrepare
 
 		m_start_clock = fb_utils::query_performance_counter();
 
-		static const char empty_string[] = "";
-		if (!string)
-		{
-			m_string = empty_string;
-			m_string_len = 0;
-		}
+		if (m_string == nullptr)
+			traceEmptyStatement();
 		else if (m_string_len == 0)
+		{
 			m_string_len = fb_strlen(m_string);
+			if (m_string_len == 0)
+				traceEmptyStatement();
+		}
 	}
 
 	~TraceDSQLPrepare()
@@ -100,6 +100,15 @@ class TraceDSQLPrepare
 	}
 
 private:
+	void traceEmptyStatement()
+	{
+		static constexpr const char* empty_string = "<empty statement>";
+		static FB_SIZE_T empty_string_length = fb_strlen(empty_string);
+
+		m_string = empty_string;
+		m_string_len = empty_string_length;
+	}
+
 	bool m_need_trace;
 	Attachment* m_attachment;
 	jrd_tra* const m_transaction;