Do not retrieve call stacks if sampling is not requested.

public/client/TracySysTrace.cpp

@@ -409,6 +409,7 @@ bool SysTraceStart( int64_t& samplingPeriod )
         return false;
     }
 
+#ifndef TRACY_NO_SAMPLING
     if( isOs64Bit )
     {
         CLASSIC_EVENT_ID stackId[2] = {};
@@ -423,6 +424,7 @@ bool SysTraceStart( int64_t& samplingPeriod )
             return false;
         }
     }
+#endif
 
 #ifdef UNICODE
     WCHAR KernelLoggerName[sizeof( KERNEL_LOGGER_NAME )];