patch 9.1.1204: MS-Windows: crash when passing long string to expand()

Problem:  MS-Windows: crash when passing long string to expand() with
          'wildignorecase'.
Solution: Use the same buflen as unix_expandpath() in dos_expandpath().
          Remove an unnecessary STRLEN() while at it (zeertzjq).

closes: #16896

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/proto/filepath.pro b/src/proto/filepath.pro
index 2979b73..260f407 100644
--- a/src/proto/filepath.pro
+++ b/src/proto/filepath.pro
@@ -55,7 +55,7 @@
 int expand_wildcards_eval(char_u **pat, int *num_file, char_u ***file, int flags);
 int expand_wildcards(int num_pat, char_u **pat, int *num_files, char_u ***files, int flags);
 int match_suffix(char_u *fname);
-int unix_expandpath(garray_T *gap, char_u *path, int wildoff, int flags, int didstar);
+int unix_expandpath(garray_T *gap, char_u *path, size_t wildoff, int flags, int didstar);
 int gen_expand_wildcards(int num_pat, char_u **pat, int *num_file, char_u ***file, int flags);
 void addfile(garray_T *gap, char_u *f, int flags);
 void FreeWild(int count, char_u **files);