never let getMyNodeInfo ever return null. fixes an autobug for device removal

app/src/main/aidl/com/geeksville/mesh/IMeshService.aidl

@@ -64,7 +64,8 @@ interface IMeshService {
     /// Users should not call this directly, only used internally by the MeshUtil activity
     void setDeviceAddress(String deviceAddr);
 
-    /// Get basic device hardware info about our connected radio
+    /// Get basic device hardware info about our connected radio.  Will never return NULL.  Will throw
+    /// RemoteException if no my node info is available
     MyNodeInfo getMyNodeInfo();
 
     /// Start updating the radios firmware

app/src/main/java/com/geeksville/mesh/service/MeshService.kt

@@ -1488,7 +1488,9 @@ class MeshService : Service(), Logging {
             doFirmwareUpdate()
         }
 
-        override fun getMyNodeInfo(): MyNodeInfo? = this@MeshService.myNodeInfo
+        override fun getMyNodeInfo(): MyNodeInfo = toRemoteExceptions {
+            this@MeshService.myNodeInfo ?: throw RadioNotConnectedException("No MyNodeInfo")
+        }
 
         override fun getMyId() = toRemoteExceptions { myNodeID }