Bug 1447308 - Fix LifoAlloc::isEmpty() check r=nbp

js/src/ds/LifoAlloc.h

@@ -724,13 +724,14 @@ class LifoAlloc
 
     // Return true if the LifoAlloc does not currently contain any allocations.
     bool isEmpty() const {
-        return chunks_.empty() || !chunks_.last()->empty();
+        return chunks_.empty() ||
+               (chunks_.begin() == chunks_.last() && chunks_.last()->empty());
     }
 
     // Return the number of bytes remaining to allocate in the current chunk.
     // e.g. How many bytes we can allocate before needing a new block.
     size_t availableInCurrentChunk() const {
-        if (!chunks_.empty())
+        if (chunks_.empty())
             return 0;
         return chunks_.last()->unused();
     }