Don't repeat the diff property table when clicking "show more"

Summary:
If you "chmod +x" a file and then generate a diff and click "show 20 lines" on
that diff, you get another janky copy of the property table. Render the property
table only for top-level rendering requests.

This started happening after D409, which fixed the far-more-obvious bug of these
things never showing up. We must have changed the logic at some point since this
side effect was surprising to me. :P

Test Plan:
Created a diff with changes and +x, clicked "show 20 lines".

  - Original diff had file property header table thing, showing the +x.
  - New context brought in by "show 20 lines" didn't have it anymore.

Reviewed By: jungejason
Reviewers: aran, jungejason, tuomaspelkonen
CC: aran, epriestley, jungejason
Differential Revision: 482

src/applications/differential/parser/changeset/DifferentialChangesetParser.php

@@ -54,6 +54,7 @@ class DifferentialChangesetParser {
   private $isSubparser;
 
   private $lineWidth = 80;
+  private $isTopLevel;
 
   const CACHE_VERSION = 4;
 
@@ -831,6 +832,14 @@ EOSYNTHETIC;
     $range_len    = null,
     $mask_force   = array()) {
 
+
+    // "Top level" renders are initial requests for the whole file, versus
+    // requests for a specific range generated by clicking "show more". We
+    // generate property changes and "shield" UI elements only for toplevel
+    // requests.
+    $this->isTopLevel = (($range_start === null) && ($range_len === null));
+
+
     $this->highlightEngine = new PhutilDefaultSyntaxHighlighterEngine();
     $this->highlightEngine->setConfig(
       'pygments.enabled',
@@ -894,7 +903,7 @@ EOSYNTHETIC;
     }
 
     $shield = null;
-    if ($range_start === null && $range_len === null && !$this->comments) {
+    if ($this->isTopLevel && !$this->comments) {
       if ($this->isGenerated()) {
         $shield = $this->renderShield(
           "This file contains generated code, which does not normally need ".
@@ -1344,6 +1353,12 @@ EOSYNTHETIC;
   }
 
   protected function renderPropertyChangeHeader($changeset) {
+    if (!$this->isTopLevel) {
+      // We render properties only at top level; otherwise we get multiple
+      // copies of them when a user clicks "Show More".
+      return null;
+    }
+
     $old = $changeset->getOldProperties();
     $new = $changeset->getNewProperties();