scripts: Fixed names/lines falling out of sync in diff table renderers

As a convenience, -d/--diff in our measurement scripts hides entries
that are unchanged by default.

Unfortunately this was broken during a recent refactor that ended up
filtering the line info but not the actual names.

Instead of reverting the broken part of the refactor, I've just moved the
filtering up to where we calculate the names. Hopefully this fixes the
bug while also simplifying this messy chunk of a logic a bit.

scripts/perfbd.py

@@ -662,7 +662,15 @@ def table(Result, results, diff_results=None, *,
     diff_table = {
         ','.join(str(getattr(r, k) or '') for k in by): r
         for r in diff_results or []}
-    names = list(table.keys() | diff_table.keys())
+    names = [name
+        for name in table.keys() | diff_table.keys()
+        if diff_results is None
+            or all_
+            or any(
+                types[k].ratio(
+                    getattr(table.get(name), k, None),
+                    getattr(diff_table.get(name), k, None))
+                for k in fields)]
 
     # sort again, now with diff info, note that python's sort is stable
     names.sort()
@@ -763,12 +771,6 @@ def table(Result, results, diff_results=None, *,
                 diff_r = None
             else:
                 diff_r = diff_table.get(name)
-                if not all_ and not any(
-                        types[k].ratio(
-                            getattr(r, k, None),
-                            getattr(diff_r, k, None))
-                        for k in fields):
-                    continue
             lines.append(table_entry(name, r, diff_r))
 
     # total