Merge pull request #467 from redboltz/bp_441

Backported #441 to cpp-1.4.

Author: redboltz

erb/cpp03_zone.hpp.erb

@@ -125,6 +125,7 @@ class zone {
                     ::free(c);
                     c = n;
                 } else {
+                    m_head = c;
                     break;
                 }
             }

include/msgpack/detail/cpp03_zone.hpp

@@ -125,6 +125,7 @@ class zone {
                     ::free(c);
                     c = n;
                 } else {
+                    m_head = c;
                     break;
                 }
             }