ofz#2846 null deref

Change-Id: I88b61d7a4faaed118db8df6f99cef08310c1f2eb
Reviewed-on: https://gerrit.libreoffice.org/40724Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

hwpfilter/source/hwpread.cxx

@@ -428,6 +428,13 @@ bool Picture::Read(HWPFile & hwpf)
     UpdateBBox(this);
     if( pictype != PICTYPE_DRAW )
         style.cell = reserved3;
+    else
+    {
+        //picinfo.picun read above is unioned with
+        //picinfo.picdraw and so wrote to the hdo pointer
+        //value, which is definitely not useful to us
+        picinfo.picdraw.hdo = nullptr;
+    }
 
     if (follow_block_size != 0)
     {