Style fix.

Author: joto

include/osmium/thread/pool.hpp

@@ -124,12 +124,10 @@ namespace osmium {
                 while (true) {
                     function_wrapper task;
                     m_work_queue.wait_and_pop(task);
-                    if (task) {
-                        if (task()) {
-                            // The called tasks returns true only when the
-                            // worker thread should shut down.
-                            return;
-                        }
+                    if (task && task()) {
+                        // The called tasks returns true only when the
+                        // worker thread should shut down.
+                        return;
                     }
                 }
             }