patch 9.1.1207: MS-Windows: build warning in filepath.c

Problem:  MS-Windows: build warning in filepath.c
          (after v9.1.1204)
Solution: add type cast (John Marriott)

Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/filepath.c b/src/filepath.c
index 1c15b8d..080a58e 100644
--- a/src/filepath.c
+++ b/src/filepath.c
@@ -3594,7 +3594,7 @@
     }
 
     // Scan all files in the directory with "dir/ *.*"
-    vim_snprintf(s, buflen - len, "*.*");
+    vim_snprintf((char *)s, buflen - len, "*.*");
     wn = enc_to_utf16(buf, NULL);
     if (wn != NULL)
 	hFind = FindFirstFileW(wn, &wfb);