Properly release zero-length Vectors.

Review URL: http://codereview.chromium.org/987004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4168 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/utils.h

@@ -341,8 +341,8 @@ class Vector {
   // Releases the array underlying this vector. Once disposed the
   // vector is empty.
   void Dispose() {
-    if (is_empty()) return;
     DeleteArray(start_);
+    if (is_empty()) return;
     start_ = NULL;
     length_ = 0;
   }