drawingML export: search for tab only once, not 3 times per line

Change-Id: I4255862d4bfb673dbcf871282f65aa6b1ad4616e
diff --git a/oox/source/export/drawingml.cxx b/oox/source/export/drawingml.cxx
index ff5ad3d..f3aceee 100644
--- a/oox/source/export/drawingml.cxx
+++ b/oox/source/export/drawingml.cxx
@@ -1801,8 +1801,10 @@ std::map< OString, std::vector<OString> > lcl_getAdjNames()
    bool bNotDone = aStream.ReadLine(aLine);
    while (bNotDone)
    {
        OString aKey = aLine.getToken(0, '\t');
        OString aValue = aLine.getToken(1, '\t');
        sal_Int32 nIndex = 0;
        // Each line is in a "key\tvalue" format: read the key, the rest is the value.
        OString aKey = aLine.getToken(0, '\t', nIndex);
        OString aValue = aLine.copy(nIndex);
        aRet[aKey].push_back(aValue);
        bNotDone = aStream.ReadLine(aLine);
    }