Initialize real_time_index to zero.

In the passive viewer, this value wasn't initialized.

PiperOrigin-RevId: 525760119
Change-Id: I6635270a30556600a0c51ba1d2767da226ba0440

Author: nimrod-gileadi

simulate/simulate.h

@@ -179,7 +179,7 @@ class Simulate {
   char previous_filename[kMaxFilenameLength] = "";
 
   // time synchronization
-  int real_time_index;
+  int real_time_index = 0;
   bool speed_changed = true;
   float measured_slowdown = 1.0;
   // logarithmically spaced realtime slow-down coefficients (percent)