Fix lexer for empty input.

tests/pglabtests/tst_SqlLexer.cpp

@@ -5,6 +5,19 @@
 
 using namespace testing;
 
+TEST(SqlLexer, emptyInput)
+{
+	QString input;
+	SqlLexer lexer(input, LexerState::Null);
+
+	int startpos, length;
+	BasicTokenType tokentype;
+	QString out;
+	lexer.nextBasicToken(startpos, length, tokentype, out);
+
+	ASSERT_THAT(startpos, Eq(0));
+	ASSERT_THAT(tokentype, Eq(BasicTokenType::End));
+}
 
 TEST(SqlLexer, lexer)
 {