Fixed a bug where if wfview started and the rig was in "center" spectrum

mode, the center checkbox would be checked, triggering setting the
center width per the pop-down menu. The code now disables the checkbox
signal method during the modification of the checkbox.

wfmain.cpp

@@ -1377,7 +1377,9 @@ void wfmain::receiveSpectrumData(QByteArray spectrum, double startFreq, double e
 
 void wfmain::receiveSpectrumFixedMode(bool isFixed)
 {
+    ui->scopeCenterModeChk->blockSignals(true);
     ui->scopeCenterModeChk->setChecked(!isFixed);
+    ui->scopeCenterModeChk->blockSignals(false);
 }
 
 void wfmain::handlePlotDoubleClick(QMouseEvent *me)