Fix blocking stdout/stderr capture on Windows

 - remove useless `ioctlsocket` on a file decriptor which is not a socket. See the Microsoft [_pipe documentation](https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/pipe?view=msvc-160):
   > A pipe resembles a file because it has a file pointer, a file descriptor, or both, and it can be read from or written to by using the Standard Library input and output functions. However, a pipe does not represent a specific file or device. Instead, it represents temporary storage in memory that is independent of the program's own memory and is controlled entirely by the operating system.

 - use a large buffer and use `_fstat` on the file decriptor to check if there is something to read from the pipe. This to prevent blocking. See also the Microsoft [_pipe documentation](https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/pipe?view=msvc-160):
   > All read and write operations on the pipe wait until there is enough data or enough buffer space to complete the I/O request.

Author: bellenot

bindings/jupyroot/src/IOHandler.cxx

@@ -71,15 +71,25 @@ JupyROOTExecutorHandler::JupyROOTExecutorHandler() {}
 
 static void PollImpl(FILE *stdStream, int *pipeHandle, std::string &pipeContent)
 {
+   fflush(stdStream);
+#ifdef _MSC_VER
+   char buffer[60000] = "";
+   struct _stat st;
+   _fstat(pipeHandle[0], &st);
+   if (st.st_size) {
+      _read(pipeHandle[0], buffer, 60000);
+      pipeContent += buffer;
+   }
+#else
    int buf_read;
    char ch;
-   fflush(stdStream);
    while (true) {
       buf_read = read(pipeHandle[0], &ch, 1);
       if (buf_read == 1) {
          pipeContent += ch;
       } else break;
    }
+#endif
 }
 
 void JupyROOTExecutorHandler::Poll()
@@ -94,10 +104,7 @@ static void InitCaptureImpl(int &savedStdStream, int *pipeHandle, int FILENO)
    if (pipe(pipeHandle) != 0) {
       return;
    }
-#ifdef _MSC_VER // Visual Studio
-   unsigned long mode = 1;
-   ioctlsocket(pipeHandle[0], FIONBIO, &mode);
-#else
+#ifndef _MSC_VER
    long flags_stdout = fcntl(pipeHandle[0], F_GETFL);
    if (flags_stdout == -1) return;
    flags_stdout |= O_NONBLOCK;