PlutoSDR: keep device open state consistent after close

Clear the m_open flag when closing PlutoSDR input and output
devices. Previously closeDevice() released m_deviceParams but left
m_open set, leaving the object in an inconsistent state where code
could treat a closed device as still valid.

This was exposed when reloading a running PlutoSDR device, where GUI
updates could access the partially torn-down device state.

Hopefully fixes #2833 (I don't have a windows machine to test).

Signed-off-by: Robin Getz <rgetz503@gmail.com>

plugins/samplesource/plutosdrinput/plutosdrinput.cpp

@@ -373,6 +373,8 @@ void PlutoSDRInput::closeDevice()
         delete m_deviceShared.m_deviceParams;
         m_deviceShared.m_deviceParams = 0;
     }
+
+    m_open = false;
 }
 
 void PlutoSDRInput::suspendBuddies()