cid#1357166 null pointer dereference

Change-Id: Id1db85f7f52c2b35e069a0252457959b16a2fd02
diff --git a/sw/source/uibase/dbui/dbmgr.cxx b/sw/source/uibase/dbui/dbmgr.cxx
index f69fcc2..703e3c6 100644
--- a/sw/source/uibase/dbui/dbmgr.cxx
+++ b/sw/source/uibase/dbui/dbmgr.cxx
@@ -1265,7 +1265,8 @@ bool SwDBManager::MergeMailFiles(SwWrtShell* pSourceShell,
                // sub-document, to get the correct PageDesc.
                if(!bFreezedLayouts && bCreateSingleFile)
                {
                    FreezeLayouts(pTargetShell, true);
                    if (pTargetShell)
                        FreezeLayouts(pTargetShell, true);
                    bFreezedLayouts = true;
                }
            } while( !bCancel && bNoError &&