vcl, sd: fix some TempFile leaks from vcl Graphic in cppunit tests

The problem is that utl::TempFile::GetURL() will return an empty string if
the file UCP is not available.  There will be an entry in the log file:

warn:legacy.osl:25344:1:ucb/source/core/provprox.cxx:366: UcbContentProviderProxy::getContentProvider - No provider for 'com.sun.star.ucb.FileContentProvider.

Change-Id: I2741a04cf4b8b420294ae521199706921b37e5c6