modemm17: initialize SyncWord sample buffer

Initialize samples_ during construction so the sample buffer is not left
indeterminate. The existing triggered_ state ensures the buffer is
initialized with fill() before its contents are used, so this is defensive
initialization rather than a functional fix.

Detected by cppcheck.

Signed-off-by: Robin Getz <rgetz503@gmail.com>

modemm17/Correlator.h

@@ -135,6 +135,7 @@ struct SyncWord
         float magnitude_2 = std::numeric_limits<float>::lowest()
     ) :
         sync_word_(std::move(sync_word)),
+        samples_{},
         magnitude_1_(magnitude_1),
         magnitude_2_(magnitude_2)
 	{}