Fix error report of type mismatch on inline tables (#853)

Parser did not track the location of the faulty inline table in the
document, and unmarshaler tried to the use the non-raw data field of the
AST node, both resulting into a panic when generating the parser error.

Fixes #850

unmarshaler_test.go

@@ -2466,6 +2466,12 @@ func TestIssue807(t *testing.T) {
 	require.Equal(t, "foo", m.Name)
 }
 
+func TestIssue850(t *testing.T) {
+	data := make(map[string]string)
+	err := toml.Unmarshal([]byte("foo = {}"), &data)
+	require.Error(t, err)
+}
+
 func TestUnmarshalDecodeErrors(t *testing.T) {
 	examples := []struct {
 		desc string