Clear child data when opening the pipes.

This is important both to reset the magic to 0, so that it will not
match if the structure is not explicitly set, and to initialize other
things we may add like counters and such.

src/childinfo.c

@@ -40,6 +40,8 @@ void openChildInfoPipe(void) {
         closeChildInfoPipe();
     } else if (anetNonBlock(NULL,server.child_info_pipe[0]) != ANET_OK) {
         closeChildInfoPipe();
+    } else {
+        memset(&server.child_info_data,0,sizeof(server.child_info_data));
     }
 }