Fix validation problems pointed out by CppunitTest_sd_export_tests

Regression from e8bdd388
(fdo#83751-FILESAVE:Custom Properties dropped while exporting to .pptx,
2014-09-11), there were two problems here:

1) Using the wrong filter when the output is expected to be suitable for
validation.

2) Writing empty custom property values, which is not valid.

Change-Id: Ic18c789c53bd40cc8aa07385cb5fd0d5c7ada6ab

oox/source/core/xmlfilterbase.cxx

@@ -713,6 +713,10 @@ writeCustomProperties( XmlFilterBase& rSelf, Reference< XDocumentProperties > xP
     {
         if ( !aprop[n].Name.isEmpty() )
         {
+            // Ignore empty string property as well.
+            if (aprop[n].Value.has<OUString>() && aprop[n].Value.get<OUString>().isEmpty())
+                continue;
+
             OString aName = OUStringToOString( aprop[n].Name, RTL_TEXTENCODING_ASCII_US );
             // pid starts from 2 not from 1 as MS supports pid from 2
             OString pid =  OUStringToOString( OUString::number(n + 2), RTL_TEXTENCODING_ASCII_US );

sd/qa/unit/sdmodeltestbase.hxx

@@ -56,7 +56,7 @@ FileFormat aFileFormats[] =
 {
     { "odp",  "impress8", "impress8", "", ODP_FORMAT_TYPE },
     { "ppt",  "MS PowerPoint 97", "Microsoft PowerPoint 97/2000/XP/2003", "sdfilt", PPT_FORMAT_TYPE },
-    { "pptx", "Impress MS PowerPoint 2007 XML", "MS PowerPoint 2007 XML", "", PPTX_FORMAT_TYPE },
+    { "pptx", "Impress Office Open XML", "Office Open XML Presentation", "", PPTX_FORMAT_TYPE },
     { "html", "graphic_HTML", "graphic_HTML", "", HTML_FORMAT_TYPE },
     { 0, 0, 0, 0, 0 }
 };