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):