notification: Initialise message

[FintasticMan]

Prevents reading uninitialised memory if notification gets cut off due to being more than 100 chars. The last character is assumed to be \0, but it is actually uninitialised.

[github-actions[bot]]

Build size and comparison to main:	Section	Size	Difference
text	406716B	80B
data	940B	0B
bss	53568B	0B

[Riksu9000]

Can you show where and how this issue occurs, so we can verify it?

[FintasticMan]

I don't think that this has ever caused an issue, but if a message gets sent to the watch with more than 100 chars, the first 100 are copied, where the last of those won't be a null-terminator. To solve that, the message array holds 101 chars, so that the last one will be a null-terminator. Except because it's not initialised, it is technically an indeterminate value unless explicitly written to.

This is just a memory safety change, and both AlertNotificationClient and AlertNotificationServer already explicitly add a trailing null-terminator (but I think they don't make use of that extra char stored in the array). We could instead trust that people writing code that sends notifications will remember to add the extra null-terminator if the message is too big.

[Riksu9000]

It would still be assuming that the struct is being used in the correct way. Someone could still fill the entire array. Maybe the public notification struct should use an std::string, which when pushing the notification would then be converted to a private format which uses a char array in a safe way.