[ghex] hex-doc: Add sanity checks to _get_buffer and _get_file in public API

[Logan Rathbone <larathbone src gnome org>]

commit f52d15b4eab0e65dbb7bc881c97d29b8ab5f2659
Author: Logan Rathbone <poprocks gmail com>
Date:   Sun Jun 26 14:54:24 2022 -0400

    hex-doc: Add sanity checks to _get_buffer and _get_file in public API

 src/hex-document.c | 4 ++++
 1 file changed, 4 insertions(+)
---
diff --git a/src/hex-document.c b/src/hex-document.c
index 465cfe0..bde30d5 100644
--- a/src/hex-document.c
+++ b/src/hex-document.c
@@ -1885,6 +1885,8 @@ hex_document_get_undo_data (HexDocument *doc)
 HexBuffer *
 hex_document_get_buffer (HexDocument *doc)
 {
+       g_return_val_if_fail (HEX_IS_DOCUMENT (doc), NULL);
+
        return doc->buffer;
 }
 
@@ -1900,6 +1902,8 @@ hex_document_get_buffer (HexDocument *doc)
 GFile *
 hex_document_get_file (HexDocument *doc)
 {
+       g_return_val_if_fail (HEX_IS_DOCUMENT (doc), NULL);
+
        return doc->file;
 }