NVMeBasicContext: Don't poll the sensor if it's not available

This avoids a flood of log messages if the system isn't in the right
state.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Change-Id: I2db6ab05c1eff5b4d2d9c95981dfe34352916652
diff --git a/src/NVMeBasicContext.cpp b/src/NVMeBasicContext.cpp
index 2287431..3c8b74d 100644
--- a/src/NVMeBasicContext.cpp
+++ b/src/NVMeBasicContext.cpp
@@ -292,6 +292,13 @@
 
     std::shared_ptr<NVMeSensor>& sensor = sensors.front();
 
+    if (!sensor->readingStateGood())
+    {
+        sensor->markAvailable(false);
+        sensor->updateValue(std::numeric_limits<double>::quiet_NaN());
+        return;
+    }
+
     /* Ensure sensor query parameters are sensible */
     if (sensor->bus < 0)
     {