ash: seek to EOF when file is opened for append

This shouldn't be necessary but without it the offset becomes
zero when an external command is run.

   rm -f log
   echo 1234567890 >>log
   cmd /c echo hi >>log
   echo 1234567890 >>log

Before this change log would contain:

   hi
   567890
   1234567890

1 files changed, 3 insertions, 0 deletions

diff --git a/shell/ash.c b/shell/ash.c
index 578904478..34d5af446 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -5455,6 +5455,9 @@ openredirect(union node *redir)
                 f = open(fname, O_WRONLY|O_CREAT|O_APPEND, 0666);
                 if (f < 0)
                         goto ecreate;
+#if ENABLE_PLATFORM_MINGW32
+                lseek(f, 0, SEEK_END);
+#endif
                 break;
         default:
 #if DEBUG