do not crash if lpstat fails

cups-pdf-postprocess.py

@@ -78,11 +78,14 @@ class CPP(QWidget):
     self._printers = self._config.get("printers", [])
     self._printers.append(("Save as ...", self._save_as_file))
 
-    for l in sp.check_output(["lpstat", "-a"]).decode("UTF-8").split("\n"):
-      p = l.split(" ")[0]
-      if p == "":
-        continue
-      self._printers.append((p, ["lp", "-d", p]))
+    try:
+      for l in sp.check_output(["lpstat", "-a"]).decode("UTF-8").split("\n"):
+        p = l.split(" ")[0]
+        if p == "":
+          continue
+        self._printers.append((p, ["lp", "-d", p]))
+    except:
+      pass
 
 
   def init_gui(self):