select: Return null for non-exiting column indexes (#13196)

Fixes #13186

internal/s3select/select_test.go

@@ -675,6 +675,11 @@ func TestCSVQueries2(t *testing.T) {
 			query:      `SELECT num2 from s3object s WHERE num2 = 0.765111`,
 			wantResult: `{"num2":" 0.765111"}`,
 		},
+		{
+			name:       "select-non_exiting_values",
+			query:      `SELECT _1 as first, s._100 from s3object s LIMIT 1`,
+			wantResult: `{"first":"1","_100":null}`,
+		},
 	}
 
 	defRequest := `<?xml version="1.0" encoding="UTF-8"?>