fix BigPtrArray pretty printer

after commit 64079184cc06444e9dfdb55a5c66829e929d4a59
"improve useuniqueptr loplugin to find arrays"

Change-Id: I29841af65fcb0c1f92e52d9aeee164328bbb4663

solenv/gdb/libreoffice/sw.py

@@ -194,7 +194,7 @@ class BigPtrArrayPrinter(object):
     class _iterator(six.Iterator):
 
         def __init__(self, array):
-            self.blocks = array['m_ppInf']
+            self.blocks = array['m_ppInf']['_M_t']['_M_head_impl']
             self.count = array['m_nSize']
             self.pos = 0
             self.block_count = array['m_nBlock']