[modules/pulseaudio] Ignore errors when starting pulseaudio daemon

This does not really solve the issue indicated in the ticket, but at
least it should leave the user with a working bar.

see #108

bumblebee/modules/pulseaudio.py

@@ -22,7 +22,10 @@ class Module(bumblebee.engine.Module):
         super(Module, self).__init__(engine, config,
             bumblebee.output.Widget(full_text=self.volume)
         )
-        bumblebee.util.execute("pulseaudio --start")
+        try:
+            bumblebee.util.execute("pulseaudio --start")
+        except Exception:
+            pass
 
         self._left = 0
         self._right = 0