CameraCalibrator warns in case no R1 data is present

[maxnoe]

Describe the bug

When running ctapipe-process on DL0 input, the CameraCalibrator throws a warning (python warning, not log message):

ctapipe/camera/calibrator.py:159: UserWarning: Encountered an event with no R1 data. DL0 is unchanged in this circumstance.

However, this is the expected case for almost anything (after all, ctapipe really starts at DL0), there shouldn't be a warning for the expected case.

[LukasNickel]

There are actually booleans defining whether or not the warnings for missing R1/DL0 should be emitted.
And for some reason they are set to True if the Calibrator encountered an event without R1/DL0:

ctapipe/ctapipe/calib/camera/calibrator.py

Lines 155 to 165 in b9b2a1a

	def _check_r1_empty(self, waveforms):
	if waveforms is None:
	if not self._r1_empty_warn:
	warnings.warn(
	"Encountered an event with no R1 data. "
	"DL0 is unchanged in this circumstance."
	)
	self._r1_empty_warn = True
	return True
	else:

Why would that make any sense? You don't warn when finding an event, but then make sure to emit the warning for the following events?

[maxnoe]

Why would that make any sense? You don't warn when finding an event, but then make sure to emit the warning for the following events?

It's the other way around. The name is misleading. It's only raising the warning for the first event and then not again.