Bug 523216. Check for NULL message in NPN_SetException. r=joshmoz

modules/plugin/base/src/nsNPAPIPlugin.cpp

@@ -1791,6 +1791,8 @@ _setexception(NPObject* npobj, const NPUTF8 *message)
     return;
   }
 
+  if (!message) return;
+
   if (gNPPException) {
     // If a plugin throws multiple exceptions, we'll only report the
     // last one for now.

modules/plugin/test/mochitest/test_npruntime_npnsetexception.html

@@ -39,6 +39,16 @@
       is(e, "second exception", "wrong exception thrown");
     }    
 
+    // test calling exception with NULL message
+    plugin.throwExceptionNextInvoke();
+    try {
+      plugin();
+      ok(false, "exception not thrown");
+    }
+    catch (e) {
+      is(e.message, "Error calling method on NPObject!", "wrong exception thrown");
+    }    
+
     SimpleTest.finish();
   }
   </script>