Invert `getattr()` check for `get_mkt_pairs()` ep

Such that we `return` early when not defined by the provider backend to
reduce an indent level in `SymbologyCache.load()`.

piker/data/_symcache.py

@@ -31,6 +31,7 @@ from pathlib import Path
 from pprint import pformat
 from typing import (
     Any,
+    Callable,
     Sequence,
     Hashable,
     TYPE_CHECKING,
@@ -56,7 +57,7 @@ from piker.brokers import (
 )
 
 if TYPE_CHECKING:
-    from ..accounting import (
+    from piker.accounting import (
         Asset,
         MktPair,
     )
@@ -149,19 +150,36 @@ class SymbologyCache(Struct):
                     'Implement `Client.get_assets()`!'
                 )
 
-            if get_mkt_pairs := getattr(client, 'get_mkt_pairs', None):
+            get_mkt_pairs: Callable|None = getattr(
+                client,
+                'get_mkt_pairs',
+                None,
+            )
+            if not get_mkt_pairs:
+                log.warning(
+                    'No symbology cache `Pair` support for `{provider}`..\n'
+                    'Implement `Client.get_mkt_pairs()`!'
+                )
+                return self
 
             pairs: dict[str, Struct] = await get_mkt_pairs()
-                for bs_fqme, pair in pairs.items():
+            if not pairs:
+                log.warning(
+                    'No pairs from intial {provider!r} sym-cache request?\n\n'
+                    '`Client.get_mkt_pairs()` -> {pairs!r} ?'
+                )
+                return self
 
-                    # NOTE: every backend defined pair should
-                    # declare it's ns path for roundtrip
-                    # serialization lookup.
+            for bs_fqme, pair in pairs.items():
                 if not getattr(pair, 'ns_path', None):
+                    # XXX: every backend defined pair must declare
+                    # a `.ns_path: tractor.NamespacePath` to enable
+                    # roundtrip serialization lookup from a local
+                    # cache file.
                     raise TypeError(
                         f'Pair-struct for {self.mod.name} MUST define a '
-                            '`.ns_path: str`!\n'
-                            f'{pair}'
+                        '`.ns_path: str`!\n\n'
+                        f'{pair!r}'
                     )
 
                 entry = await self.mod.get_mkt_info(pair.bs_fqme)
@@ -195,12 +213,6 @@ class SymbologyCache(Struct):
                 pair,
             )
 
-            else:
-                log.warning(
-                    'No symbology cache `Pair` support for `{provider}`..\n'
-                    'Implement `Client.get_mkt_pairs()`!'
-                )
-
         return self
 
     @classmethod