tdf#119136 GetPropertyFromStyleSheet infinite loop

So, apparently we accept a style that has no styleId and
define it as such. Due to some reworkings, this function
was called instead. Since we can "find" a style without a
name, now every parentless style thought it inherited from
this nameless style.

Change-Id: I47b4119abd37ece94a39e636ddb7798b809ccb04
Reviewed-on: https://gerrit.libreoffice.org/58705
Tested-by: Jenkins
Reviewed-by: Justin Luth <justin_luth@sil.org>

writerfilter/source/dmapper/DomainMapper_Impl.cxx

@@ -713,7 +713,9 @@ uno::Any DomainMapper_Impl::GetPropertyFromStyleSheet(PropertyIds eId)
             }
         }
         //search until the property is set or no parent is available
-        StyleSheetEntryPtr pNewEntry = GetStyleSheetTable()->FindStyleSheetByISTD(pEntry->sBaseStyleIdentifier);
+        StyleSheetEntryPtr pNewEntry;
+        if ( !pEntry->sBaseStyleIdentifier.isEmpty() )
+            pNewEntry = GetStyleSheetTable()->FindStyleSheetByISTD(pEntry->sBaseStyleIdentifier);
 
         SAL_WARN_IF( pEntry == pNewEntry, "writerfilter.dmapper", "circular loop in style hierarchy?");