LibSQL: Report a syntax error for unsupported LIMIT clause syntax

Rather than aborting when a LIMIT clause of the form 'LIMIT expr, expr'
is encountered, fail the parser with a syntax error. This will be nicer
for the user and fixes the following fuzzer bug:
https://crbug.com/oss-fuzz/34837

Tests/LibSQL/TestSqlStatementParser.cpp

@@ -547,6 +547,7 @@ TEST_CASE(select)
  EXPECT(parse("SELECT * FROM table LIMIT 12").is_error());
  EXPECT(parse("SELECT * FROM table LIMIT 12 OFFSET;").is_error());
  EXPECT(parse("SELECT * FROM table LIMIT 12 OFFSET 15").is_error());
+ EXPECT(parse("SELECT * FROM table LIMIT 15, 16;").is_error());
 
  struct Type {
  SQL::ResultType type;

Userland/Libraries/LibSQL/Parser.cpp

@@ -321,11 +321,11 @@ NonnullRefPtr<Select> Parser::parse_select_statement(RefPtr<CommonTableExpressio
  RefPtr<Expression> offset_expression;
  if (consume_if(TokenType::Offset)) {
  offset_expression = parse_expression();
- } else {
+ } else if (consume_if(TokenType::Comma)) {
  // Note: The limit clause may instead be defined as "offset-expression, limit-expression", effectively reversing the
  // order of the expressions. SQLite notes "this is counter-intuitive" and "to avoid confusion, programmers are strongly
  // encouraged to ... avoid using a LIMIT clause with a comma-separated offset."
- VERIFY(!consume_if(TokenType::Comma));
+ syntax_error("LIMIT clauses of the form 'LIMIT <expr>, <expr>' are not supported");
  }
 
  limit_clause = create_ast_node<LimitClause>(move(limit_expression), move(offset_expression));