re-add some gdb BigPtrArray pretty printing

After commit c6902761
"Revert "use std::vector in BigPtrArray""

<mst_> noelgrandin: you reverted both gdb changes but only one sw
change?
<noelgrandin> mst_, I thought your gdb change only appliled to the
std::vector?
<mst_> noelgrandin: there was another std::something or other change
there, one was mvInfo and the other mvData
<noelgrandin> mst_, sigh, will fix that

Change-Id: I3059d29b1a559eb3077f5d713be011e15e887ee0

solenv/gdb/libreoffice/sw.py

@@ -246,7 +246,7 @@ class BigPtrArrayPrinter(object):
                 raise StopIteration()
 
             name = str(self.pos)
-            node = self.block['pData'][self.pos - self.block['nStart']]
+            node = self.block['mvData']['_M_elems'][self.pos - self.block['nStart']]
             value =  self._node_value(node)
             if self.pos == self.block['nEnd']:
                 self._next_block()