auto judge bw when setting sprate

uhd_cpp/uhd_spectrum/specwidget.ui

@@ -326,7 +326,7 @@
        <item row="6" column="1">
         <widget class="QSpinBox" name="spinBox_bw">
          <property name="minimum">
-          <number>200</number>
+          <number>0</number>
          </property>
          <property name="maximum">
           <number>200000</number>

uhd_cpp/uhd_spectrum/uhd_device_win32.cpp

@@ -280,8 +280,8 @@ double  uhd_device::set_sample_rate(const double sprate)
 		double bw = sprate;
 		if (bw >56e6)
 			bw = 56e6;
-		if (bw <200000)
-			bw = 200000;
+		if (bw <200000 || bw > sprate)
+			bw = sprate;
 		fprintf(stderr, "Setting RX Rate: %f...\n", sprate);
 		UHD_DO(uhd_usrp_set_rx_rate(usrp, sprate, m_channel));
 
@@ -323,6 +323,14 @@ double uhd_device::set_rx_bandwidth(double bw)
 {
 	if (usrp)
 	{
+		double srate = 0;
+		// See what rate actually is
+		UHD_DO(uhd_usrp_get_rx_rate(usrp, m_channel, &srate));
+		fprintf(stderr, "Current RX Rate: %f...\n", srate);
+
+		if (bw < 200000 || bw >=srate)
+			bw = srate;
+
 		fprintf(stderr, "Setting RX Bandwidth: %f MHz...\n", bw/1e6);
 		UHD_DO(uhd_usrp_set_rx_bandwidth(usrp, bw, m_channel));