tool_cb_wrt: fix write output for very old Windows versions

- Pass missing parameter for 'lpNumberOfCharsWritten' to WriteConsoleW()
  function.

Apparently this parameter was *not* optional on older Windows versions.

Issue observed on Windows XP SP2. Issue not observed on Windows 7 SP1.
So at some point between those two Microsoft changed the behavior.

Prior to this change, on those versions if parameter is NULL then the
function call fails with error ERROR_INVALID_ACCESS.

Regression since af3f4e41.

Ref: https://github.com/MicrosoftDocs/Console-Docs/issues/299

Fixes https://github.com/curl/curl/issues/12131
Closes https://github.com/curl/curl/pull/12130

src/tool_cb_wrt.c

@@ -237,7 +237,7 @@ size_t tool_write_cb(char *buffer, size_t sz, size_t nmemb, void *userdata)
   if(isatty(fileno(outs->stream)) &&
      GetConsoleScreenBufferInfo((HANDLE)fhnd, &console_info)) {
     wchar_t *wc_buf;
-    DWORD wc_len;
+    DWORD wc_len, chars_written;
     unsigned char *rbuf = (unsigned char *)buffer;
     DWORD rlen = (DWORD)bytes;
 
@@ -292,7 +292,7 @@ size_t tool_write_cb(char *buffer, size_t sz, size_t nmemb, void *userdata)
               (HANDLE) fhnd,
               prefix,
               prefix[1] ? 2 : 1,
-              NULL,
+              &chars_written,
               NULL)) {
             return CURL_WRITEFUNC_ERROR;
           }
@@ -351,7 +351,7 @@ size_t tool_write_cb(char *buffer, size_t sz, size_t nmemb, void *userdata)
           (HANDLE) fhnd,
           wc_buf,
           wc_len,
-          NULL,
+          &chars_written,
           NULL)) {
         free(wc_buf);
         return CURL_WRITEFUNC_ERROR;