PCKPacker: Fix first file being written mis-aligned

[nikitalita]

cc @bruvzg

In #105757 , when we changed the PCK format to have the directory come at the end of the files rather than before, we failed to account for the header size potentially causing misalignment on the first file. The header size is currently 104 bytes, so the default alignment of 32 would be not be respected for the first file. This PR fixes that by padding the header so that the file base starts at an aligned byte.

[bruvzg]

The same should be added to EditorExportPlatform::save_pack():

diff --git a/editor/export/editor_export_platform.cpp b/editor/export/editor_export_platform.cpp
index 0ab65408f2..62aca2990b 100644
--- a/editor/export/editor_export_platform.cpp
+++ b/editor/export/editor_export_platform.cpp
@@ -1966,6 +1966,11 @@ Error EditorExportPlatform::save_pack(const Ref<EditorExportPreset> &p_preset, b
                f->store_32(0); // Reserved.
        }

+       int file_padding = _get_pad(PCK_PADDING, f->get_position());
+       for (int i = 0; i < file_padding; i++) {
+               f->store_8(0);
+       }
+
        uint64_t file_base = f->get_position();
        f->seek(file_base_ofs);

But I'm not sure if adding this padding is relevant on any of the supported platforms.

[nikitalita]

Done

[akien-mga]

Thanks!