Fix key variable not initialised (#4790)

radio/src/targets/simu/opentxsimulator.cpp

@@ -284,6 +284,9 @@ void OpenTxSimulator::rotaryEncoderEvent(int steps)
     key = KEY_MINUS;
   else if (steps < 0)
     key = KEY_PLUS;
+  else
+   // Should not happen but Clang complains that key is unset otherwise
+   return;
 
   setKey(key, 1);
 #if (QT_VERSION >= QT_VERSION_CHECK(5, 4, 0))