Make differential.querydiffs more liberal about arguments

Summary:
Fixes T12092. D17164 made `DiffQuery` more strict about arguments using modern conventions, but `differential.querydiffs` uses bizarre ancient conventions.

Give it more modern conventions instead.

Test Plan: Made a `querydiffs` call with only revision IDs.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T12092

Differential Revision: https://secure.phabricator.com/D17172

src/applications/differential/conduit/DifferentialQueryDiffsConduitAPIMethod.php

@@ -26,16 +26,27 @@ final class DifferentialQueryDiffsConduitAPIMethod
     $ids = $request->getValue('ids', array());
     $revision_ids = $request->getValue('revisionIDs', array());
 
-    $diffs = array();
-    if ($ids || $revision_ids) {
-      $diffs = id(new DifferentialDiffQuery())
-        ->setViewer($request->getUser())
-        ->withIDs($ids)
-        ->withRevisionIDs($revision_ids)
-        ->needChangesets(true)
-        ->execute();
+    if (!$ids && !$revision_ids) {
+      // This method just returns nothing if you pass no constraints because
+      // pagination hadn't been invented yet in 2008 when this method was
+      // written.
+      return array();
     }
 
+    $query = id(new DifferentialDiffQuery())
+      ->setViewer($request->getUser())
+      ->needChangesets(true);
+
+    if ($ids) {
+      $query->withIDs($ids);
+    }
+
+    if ($revision_ids) {
+      $query->withRevisionIDs($revision_ids);
+    }
+
+    $diffs = $query->execute();
+
     return mpull($diffs, 'getDiffDict', 'getID');
   }