Remove invalid assert.

The original intention was to ensure that either a ring buffer with data was
selected (sel >= 0 ), or there is no data left to process (activeNum == 0).
However, in an unlikely case that all ring buffers contain a PERF_RECORD_LOST
event, it is possible for the assert to fail, as there may still be data in
buffers, but at the same time no buffer would be selected. Buffer processing
advances the data pointers, so in the next loop iteration the results may be
different.

client/TracySysTrace.cpp

@@ -1324,7 +1324,6 @@ void SysTraceWorker( void* ptr )
                             }
                         }
                     }
-                    assert( sel >= 0 || activeNum == 0 );
                     if( sel >= 0 )
                     {
                         auto& ring = s_ring[s_ctxBufferIdx + sel];