bpo-38222: Check specifically for a drive, not just a colon (GH-25540)

diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index 7a5a0e9..85e1e69 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -1860,8 +1860,8 @@ attributes_from_dir(LPCWSTR pszFile, BY_HANDLE_FILE_INFORMATION *info, ULONG *re
         while (--n > 0 && (filename[n] == L'\\' || filename[n] == L'/')) {
             ((LPWSTR)filename)[n] = L'\0';
         }
-        if (!n || filename[n] == L':') {
-            // Nothing left te query
+        if (!n || (n == 1 && filename[1] == L':')) {
+            // Nothing left to query
             free((void *)filename);
             return FALSE;
         }