rtk/gps: fix quick double click on "connect"

When the user quickly clicked the "connect" button twice, the task to
connect to the receiver would be executed twice, causing problems.
Disable the button until the connection process is finished.

GCSViews/ConfigurationView/ConfigSerialInjectGPS.cs

@@ -482,7 +482,14 @@ public async Task DoConnect()
             } 
             else if (chk_autoconfig.Checked && comboBoxConfigType.Text == "Septentrio")
             {
-                await ConfigureSeptentrioReceiver();
+                BUT_connect.Enabled = false;
+                try
+                {
+                    await ConfigureSeptentrioReceiver();
+                } catch (Exception ex)
+                {
+                    throw ex;
+                } finally { BUT_connect.Enabled = true; }
             }
             t12 = new System.Threading.Thread(new System.Threading.ThreadStart(mainloop))
             {