Fix issue with single realization when using resdata (#12737)

* Moves multi reader initialization
* Log error message if not able to open file
* Make keywordCount pure virtual

The base class `RifSummaryReaderInterface` is changed to be abstract and the `keywordCount` is declared as a pure virtual method, therefore the derived classes must implement the method.

This will ensure that all readers are responsible for reporting a keyword count.

* Ensures addresses are created if required

Calls `createAddressesIfRequired` on the summary reader to ensure addresses are created before accessing keyword count.
This prevents potential issues when the addresses haven't been initialized yet.

ApplicationLibCode/ProjectDataModel/Summary/RimFileSummaryCase.cpp

@@ -100,7 +100,7 @@ void RimFileSummaryCase::createSummaryReaderInterfaceThreadSafe( RifEnsembleImpo
     //
     // https://github.com/OPM/ResInsight/issues/11342
 
-    m_multiSummaryReader        = std::make_unique<RifMultipleSummaryReaders>();
+    auto multiReader            = std::make_unique<RifMultipleSummaryReaders>();
     m_fileSummaryReaderId       = -1;
     m_additionalSummaryReaderId = -1;
 
@@ -112,6 +112,7 @@ void RimFileSummaryCase::createSummaryReaderInterfaceThreadSafe( RifEnsembleImpo
 
     m_fileSummaryReaderId = reader->serialNumber();
 
+    m_multiSummaryReader = std::move( multiReader );
     m_multiSummaryReader->addReader( std::move( reader ) );
 
     openAndAttachAdditionalReader();