SHP: Fix unreported issue with spatialindex

When the spatialindex did not exist and it is created
when the file is in edit mode the spatialindex was not
recreated when editing finshed.

Followup: #53186

src/core/providers/ogr/qgsogrprovider.cpp

@@ -2991,7 +2991,8 @@ bool QgsOgrProvider::createSpatialIndexImpl()
 
     QFileInfo fi( mFilePath );     // to get the base name
     //find out, if the .qix file is there
-    return QFileInfo::exists( fi.path().append( '/' ).append( fi.completeBaseName() ).append( ".qix" ) );
+    mShapefileHadSpatialIndex = QFileInfo::exists( fi.path().append( '/' ).append( fi.completeBaseName() ).append( ".qix" ) );
+    return mShapefileHadSpatialIndex;
   }
   else if ( mGDALDriverName == QLatin1String( "GPKG" ) ||
             mGDALDriverName == QLatin1String( "SQLite" ) )