Ingest: Exit if child process redirect io failed (#2540)

* 修复子进程无法打开日志输出重定向导致的fork错误

srs进程fork后，未能输出重定向而返回错误，导致fork的子进程未能出。

* remove the var child_err

* Fixed IO redirection error detection

* Fixed BUG where lost during logs on normal start

trunk/src/app/srs_app_process.hpp

@@ -53,6 +53,9 @@ public:
     // @param argv the argv for binary path, the argv[0] generally is the binary.
     // @remark the argv[0] must be the binary.
     virtual srs_error_t initialize(std::string binary, std::vector<std::string> argv);
+private:
+    // Redirect standard I/O.
+    virtual srs_error_t redirect_io();
 public:
     // Start the process, ignore when already started.
     virtual srs_error_t start();