algo: Fix read of unitialized memory in DigiEvent.

@v.friese, this points to a potential issue in the event builder. Currently the event number is not set there, so this field stays uninitialized.

algo/base/DigiData.h

@@ -69,8 +69,9 @@ namespace cbm::algo
    * @note Uses PODVector for storage, so memory is not initialized by default.
    */
   struct DigiEvent : public DigiData {
-    uint64_t fNumber;  ///< Event identifier
-    double fTime;      ///< Event trigger time [ns]
+    // FIXME: Event number not set yet!
+    uint64_t fNumber = -1;  ///< Event identifier
+    double fTime     = 0;   ///< Event trigger time [ns]
 
     static std::vector<DigiEvent> FromCbmDigiEvents(const std::vector<CbmDigiEvent>& events);
     static std::vector<CbmDigiEvent> ToCbmDigiEvents(const std::vector<DigiEvent>& events);