fix: mark when we exit a trace

* src/datadog/trace_segment.cpp: Here.

Author: elsa

src/datadog/trace_segment.cpp

@@ -9,6 +9,7 @@
 #include <datadog/telemetry/metrics.h>
 #include <datadog/telemetry/telemetry.h>
 #include <datadog/trace_segment.h>
+#include <datadog/tracer.h>
 
 #include <cassert>
 #include <string>
@@ -244,6 +245,11 @@ void TraceSegment::span_finished() {
     }
   }
 
+#ifdef __linux__
+  // When all spans are finished, so is the current trace.
+  elastic_apm_profiling_correlation_tls_v1->trace_present = 0;
+#endif
+
   telemetry::metrics().tracer.trace_segments_closed.inc();
 }