Ensure we delete media if we reject due to spam check (#17246)

Fixes up #17239

We need to keep the spam check within the `try/except` block. Also makes
it so that we don't enter the top span twice.

Also also ensures that we get the right thumbnail length.

changelog.d/17246.misc

@@ -0,0 +1 @@
+Fix errors in logs about closing incorrect logging contexts when media gets rejected by a module.

synapse/media/media_repository.py

@@ -1049,6 +1049,11 @@ class MediaRepository:
                     finally:
                         t_byte_source.close()
 
+                    # We flush and close the file to ensure that the bytes have
+                    # been written before getting the size.
+                    f.flush()
+                    f.close()
+
                     t_len = os.path.getsize(fname)
 
                     # Write to database

synapse/media/media_storage.py

@@ -137,24 +137,11 @@ class MediaStorage:
         dirname = os.path.dirname(fname)
         os.makedirs(dirname, exist_ok=True)
 
-        main_media_repo_write_trace_scope = start_active_span(
-            "writing to main media repo"
-        )
-        main_media_repo_write_trace_scope.__enter__()
-
-        with main_media_repo_write_trace_scope:
         try:
+            with start_active_span("writing to main media repo"):
                 with open(fname, "wb") as f:
                     yield f, fname
 
-            except Exception as e:
-                try:
-                    os.remove(fname)
-                except Exception:
-                    pass
-
-                raise e from None
-
             with start_active_span("writing to other storage providers"):
                 spam_check = (
                     await self._spam_checker_module_callbacks.check_media_file_for_spam(
@@ -174,6 +161,14 @@ class MediaStorage:
                     with start_active_span(str(provider)):
                         await provider.store_file(path, file_info)
 
+        except Exception as e:
+            try:
+                os.remove(fname)
+            except Exception:
+                pass
+
+            raise e from None
+
     async def fetch_media(self, file_info: FileInfo) -> Optional[Responder]:
         """Attempts to fetch media described by file_info from the local cache
         and configured storage providers.