Add error handling for invalid if condition and test for crash with null byte

Author: antonmedv

expr_test.go

@@ -2683,6 +2683,12 @@ func TestExpr_crash(t *testing.T) {
 	require.Error(t, err)
 }
 
+func TestExpr_crash_with_zero(t *testing.T) {
+	code := "if\x00"
+	_, err := expr.Compile(code)
+	require.Error(t, err)
+}
+
 func TestExpr_nil_op_str(t *testing.T) {
 	// Let's test operators, which do `.(string)` in VM, also check for nil.
 

parser/parser.go

@@ -329,6 +329,9 @@ func (p *Parser) parseVariableDeclaration() Node {
 
 func (p *Parser) parseConditionalIf() Node {
 	p.next()
+	if p.err != nil {
+		return nil
+	}
 	nodeCondition := p.parseExpression(0)
 	p.expect(Bracket, "{")
 	expr1 := p.parseSequenceExpression()