vcl: remove alloca() in UniscribeLayout::GetCaretPositions()

Change-Id: I0caab3b69b10aba6a5d45a11f8e9724b4d3c6d83

vcl/win/source/gdi/winlayout.cxx

@@ -1873,7 +1873,7 @@ void UniscribeLayout::GetCaretPositions( int nMaxIdx, long* pCaretXArray ) const
     int i;
     for( i = 0; i < nMaxIdx; ++i )
         pCaretXArray[ i ] = -1;
-    long* const pGlyphPos = (long*)alloca( (mnGlyphCount+1) * sizeof(long) );
+    std::unique_ptr<long[]> const pGlyphPos = new long[mnGlyphCount + 1];
     for( i = 0; i <= mnGlyphCount; ++i )
         pGlyphPos[ i ] = -1;