Attempt to detect sound system access problem

Fixes #232

app/musicmuster.py

@@ -211,7 +211,13 @@ class Window(QMainWindow, Ui_MainWindow):
         self.txtSearch.setHidden(True)
         self.statusbar.addWidget(self.txtSearch)
         self.hide_played_tracks = False
-        mixer.init()
+        try:
+            mixer.init()
+        except Exception:
+            helpers.show_warning(self, "Fatal error",
+                                 "Cannot initialise sound device")
+            sys.exit(1)
+
         self.widgetFadeVolume.hideAxis("bottom")
         self.widgetFadeVolume.hideAxis("left")
         self.widgetFadeVolume.setDefaultPadding(0)