If Excel's shared string table (SST) contains the empty string not only at the beginning but also redundantly at a further place, the following bug in the shared string table reader of class ZCL_EXCEL_READER_HUGE_FILE occurs:
Since the sXML reader was not cleared with the beginning of each node, the last read string of the table was carried over into the next string .
Added unit test ```test_shared_string_some_empty``` to reproduce the bug, and fixed it in the way proposed by Kai Walter (see Def-376)
There was a book in reading strings from the SST, caused by not catching the "node value" event in the main loop. Shared strings could point wrongly to the first table element (which usually contains the empty string).
