fix: catch missing dateTime KeyError

[yo-han]

Catch and log missing keys and indicies in the get_last_marker function.

fixes #31

[redakker]

@yo-han , Thank you for the quick fix, but comes another:

Logger: custom_components.carelink
Source: custom_components/carelink/init.py:383
Integration: carelink
First occurred: 08:23:14 (3 occurrences)
Last logged: 08:23:40

Unexpected error fetching carelink data: 'medicalDeviceInformation'
Traceback (most recent call last):
File "/usr/src/homeassistant/homeassistant/helpers/update_coordinator.py", line 258, in _async_refresh
self.data = await self._async_update_data()
File "/config/custom_components/carelink/init.py", line 383, in _async_update_data
data[SENSOR_KEY_MEDICAL_DEVICE_MANUFACTURER] = recent_data[
KeyError: 'medicalDeviceInformation'