Improve regular file detection on Windows.

Based on a suggestion by Khaled Mardam-Bey.

lib/zip_source_file_win32_named.c

diff --git a/lib/zip_source_file_win32_named.c b/lib/zip_source_file_win32_named.c
index a2a44c8..1fe5591 100644
--- a/lib/zip_source_file_win32_named.c
+++ b/lib/zip_source_file_win32_named.c
@@ -208,7 +208,14 @@
     }
 
     st->exists = true;
-    st->regular_file = true; /* TODO: Is this always right? How to determine without a HANDLE? */
+    st->regular_file = false;
+
+    if (file_attributes.dwFileAttributes != INVALID_FILE_ATTRIBUTES) {
+        if ((file_attributes.dwFileAttributes & (FILE_ATTRIBUTE_DIRECTORY | FILE_ATTRIBUTE_DEVICE | FILE_ATTRIBUTE_REPARSE_POINT)) == 0) {
+            st->regular_file = true;
+        }
+    }
+
     if (!_zip_filetime_to_time_t(file_attributes.ftLastWriteTime, &st->mtime)) {
         zip_error_set(&ctx->error, ZIP_ER_READ, ERANGE);
         return false;