Initialize degrade saved SNR setting to zero

git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@6169 ab8295b8-cf94-4d9e-aec4-7959e3be5d79

Configuration.cpp

@@ -738,6 +738,8 @@ Configuration::impl::impl (Configuration * self, QSettings * settings, QWidget *
   , setup_split_ {false}
   , required_tx_frequency_ {0}
   , enforce_mode_and_split_ {false}
+  , degrade_ {0.}               // initialize to zero each run, not
+                                // saved in settings
   , default_audio_input_device_selected_ {false}
   , default_audio_output_device_selected_ {false}
 {