[refactor] Drop the two continues in callbinrepr

Nest the truthiness checks instead of using ``continue`` to skip to
the next ``hook_result`` entry. Behaviourally identical, but each
``continue`` was being reported as a partial branch by codecov even
when both arcs were hit by tests — pytester-driven in-process tests
don't always show the ``continue → loop exit`` arc, so the partials
were sticky. With the nested form the for-loop has a single fall-
through edge and the partial disappears.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: Pierre-Sassoulas

src/_pytest/assertion/__init__.py

@@ -181,19 +181,19 @@ def callbinrepr(op, left: object, right: object) -> str | None:
             config=item.config, op=op, left=left, right=right
         )
         for new_expl in hook_result:
-            if not new_expl:
-                continue
             # Plugin-supplied lists are truncated here; the built-in
             # impl truncates as it streams, so this is a no-op on its
-            # already-short output.
-            new_expl = truncate.materialize_with_truncation(new_expl, item.config)
-            if not new_expl:
-                continue
-            new_expl = [line.replace("\n", "\\n") for line in new_expl]
-            res = "\n~".join(new_expl)
-            if item.config.getvalue("assertmode") == "rewrite":
-                res = res.replace("%", "%%")
-            return res
+            # already-short output. ``materialize_with_truncation`` can
+            # return ``[]`` when the input was a truthy-but-empty
+            # iterable, so re-check after materialising.
+            if new_expl:
+                new_expl = truncate.materialize_with_truncation(new_expl, item.config)
+                if new_expl:
+                    new_expl = [line.replace("\n", "\\n") for line in new_expl]
+                    res = "\n~".join(new_expl)
+                    if item.config.getvalue("assertmode") == "rewrite":
+                        res = res.replace("%", "%%")
+                    return res
         return None
 
     saved_assert_hooks = util._reprcompare, util._assertion_pass