notification: Initialise message

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.

src/components/ble/NotificationManager.h

@@ -30,7 +30,7 @@ namespace Pinetime {
         Id id = 0;
         bool valid = false;
         uint8_t size;
-        std::array<char, MessageSize + 1> message;
+        std::array<char, MessageSize + 1> message {};
         Categories category = Categories::Unknown;
 
         const char* Message() const;