fix: Don't crash if there's no serial ports

I have a hardware RS232 port, so always had one COM port
to add to the list of ports that might have been nogasms.
If you had no ports, the application would crash on start.

Fixes #11

NogasmChart/MainWindow.xaml.cs

@@ -57,7 +57,16 @@ public MainWindow()
 
             MenuFileSave.IsEnabled = false;
 
-            ComPort.SelectedItem = SerialPort.GetPortNames()[0];
+            if (SerialPort.GetPortNames().Any())
+            {
+                ComPort.SelectedItem = SerialPort.GetPortNames()[0];
+            }
+            else
+            {
+                ComPort.IsEnabled = false;
+                StartStop.IsEnabled = false;
+                Orgasm.IsEnabled = false;
+            }
 
             // ToDo: Make this selectable
             _analyser = new NogasmMotorDirectAnalyser();