Merge branch 'bugfix/esp_error_check_release_builds' into 'master'

fix warnings generated by ESP_ERROR_CHECK(variable) in release builds

This uses the same pattern as “assert” in release builds to silence the
warning. At the same time, we make sure that if a statement is wrapped
into ESP_ERROR_CHECK, it is executed in release build as well.

Fixes https://github.com/espressif/esp-idf/issues/497

See merge request !641