Bug 1532857 - Use SubChunkLimit when re-enabling the nursery r=jonco

I should have included this change in Bug 1527532.

Differential Revision: https://phabricator.services.mozilla.com/D22241

--HG--
extra : moz-landing-system : lando

js/src/gc/Nursery.cpp

@@ -194,7 +194,7 @@ void js::Nursery::enable() {
     if (!allocateNextChunk(0, lock)) {
       return;
     }
-    capacity_ = NurseryChunkUsableSize;
+    capacity_ = SubChunkLimit;
   }
 
   setCurrentChunk(0, true);