accounting.calc: `.error()` on bad txn-time fields..

Since i'm seeing IB records with a `None` value and i don't want to be
debugging every time order-mode boots up..

Also use `pdb=debug_mode` in `.open_ledger_dfs()`

piker/accounting/calc.py

@@ -289,15 +289,26 @@ def iter_by_dt(
             else:
                 continue
 
-        # XXX: should never get here..
+        # XXX: we should never really get here bc it means some kinda
+        # bad txn-record (field) data..
+        #
+        # -> set the `debug_mode = True` if you want to trace such
+        # cases from REPL ;)
         else:
-            with maybe_open_crash_handler(pdb=True):
-                raise ValueError(
+            debug_mode: bool = False
+            report: str = (
                 f'Invalid txn time ??\n'
                 f'txn-id: {k!r}\n'
                 f'{k!r}: {v!r}\n'
             )
-                    # assert v is not None, f'No valid value for `{k}`!?'
+            if debug_mode:
+                with maybe_open_crash_handler(
+                    pdb=debug_mode,
+                    raise_on_exit=False,
+                ):
+                    raise ValueError(report)
+            else:
+                log.error(report)
 
             if _invalid is not None:
                 _invalid.append(tx)
@@ -400,7 +411,10 @@ def open_ledger_dfs(
     can update the ledger on exit.
 
     '''
-    with maybe_open_crash_handler(pdb=debug_mode):
+    with maybe_open_crash_handler(
+        pdb=debug_mode,
+        # raise_on_exit=False,
+    ):
         if not ledger:
             import time
             from ._ledger import open_trade_ledger