[BUGFIX] [Spatialite] Finalize statement in addFeatures()

The sqlite3_prepare_v2() call in QgsSpatiaLiteProvider::addFeatures() is
not associated with a matching sqlite3_finalize(). Consequently at
time of sqlite3_close(), the later returns a SQLITE_BUSY error and
fails to close the file descriptor (can be checked by runing 'lsof' on
qgis process).

src/providers/spatialite/qgsspatialiteprovider.cpp

@@ -3748,6 +3748,9 @@ bool QgsSpatiaLiteProvider::addFeatures( QgsFeatureList & flist )
           break;
         }
       }
+
+      sqlite3_finalize( stmt );
+
       if ( ret == SQLITE_DONE || ret == SQLITE_ROW )
       {
         ret = sqlite3_exec( sqliteHandle, "COMMIT", nullptr, nullptr, &errMsg );