fix: keep a romm entry whole without a size

RomM compares file_size_bytes with the entry's size before any hash. A
new hash the truth gives no size for went out beside the old size and
was reported as a size removal. The entry now stays as written and the
correction is withheld and named.

tests/test_export_counts.py

@@ -913,7 +913,8 @@ class TheSummaryCountsWhatTheFileCarries(unittest.TestCase):
         return NativeFile(
             "scph5501.bin", "scph5501.bin", "psx",
             platform={"size": 524288, "crc32": "deadbeef", "md5": A, "sha1": "1" * 40},
-            truth={"md5": B},
+            # With a size of its own: without one, RomM keeps its entry whole.
+            truth={"md5": B, "size": 524288},
         )
 
     def test_romm_drops_the_hashes_it_counts_cleared(self):

tests/test_exporters.py

@@ -1509,9 +1509,17 @@ class RommSizeIsNeverNone(unittest.TestCase):
         produced = exporter.render(systems, report, {}, None)
         return exporter, systems, produced, json.loads(produced["known_bios_files.json"])
 
-    def test_the_platform_size_stands_when_none_is_settled(self):
-        _, _, _, data = self._export(524288)
-        self.assertEqual(data["psx:scph5501.bin"]["size"], "524288")
+    def test_an_entry_the_truth_takes_without_a_size_stays_whole(self):
+        """RomM compares the size before any hash: the new md5 beside the
+        old size never verified, and the report said the size was removed."""
+        from export_native import landed_changes  # noqa: PLC0415
+
+        exporter, systems, _, data = self._export(524288)
+        self.assertEqual(
+            data["psx:scph5501.bin"], {"size": "524288", "md5": "a" * 32}
+        )
+        self.assertEqual(landed_changes(exporter, systems).records, [])
+        self.assertEqual(len(exporter.withheld()), 1)
 
     def test_no_size_is_written_rather_than_none(self):
         exporter, systems, produced, data = self._export(None)