libbb: copy entire match during tab-completion

Because tab-completion is case-insensitive the matching text might
differ from what the user typed.  Insert the whole of the matching
text, not just the tail.  Thus:

   $ cd doc<TAB>

now expands to:

   $ cd Documents/

1 files changed, 4 insertions, 0 deletions

diff --git a/libbb/lineedit.c b/libbb/lineedit.c
index 0ec9baa5f..95f92aa75 100644
--- a/libbb/lineedit.c
+++ b/libbb/lineedit.c
@@ -1317,7 +1317,11 @@ static NOINLINE void input_tab(smallint *lastWasTab)
                 /* save tail */
                 strcpy(match_buf, &command_ps[cursor]);
                 /* add match and tail */
+#if ENABLE_PLATFORM_MINGW32
+                sprintf(&command_ps[cursor-match_pfx_len], "%s%s", chosen_match, match_buf);
+#else
                 sprintf(&command_ps[cursor], "%s%s", chosen_match + match_pfx_len, match_buf);
+#endif
                 command_len = strlen(command_ps);
                 /* new pos */
                 pos = cursor + len_found - match_pfx_len;