Make zoom reset more reliable

Especially at higher zooms, right click on the freq axis did not fully
reset the zoom level on the fft dock. Add an emit to resetHorizontalZoom()
as is done already in zoomStepX().

Signed-off-by: Jeff Long <willcode4@gmail.com>

Author: willcode

src/qtgui/plotter.cpp

@@ -1665,6 +1665,7 @@ void CPlotter::resetHorizontalZoom(void)
 {
     setFftCenterFreq(0);
     setSpanFreq((qint32)m_SampleFreq);
+    emit newZoomLevel(1.0);
 }
 
 /** Center FFT plot around 0 (corresponds to center freq). */