CsvTokenizer - add additional test case for escaped quotes

It simulates the case where csv fields are fully quoted and an escaped
quote ("") is found in some field. This case is handled correctly,
adding the test to guard this in potential future modifications.

gnucash/import-export/csv-imp/test/test-tokenizer.cpp

@@ -178,6 +178,7 @@ static tokenize_csv_test_data comma_separated [] = {
         { "Test\\ with backslash,nextfield", 2, { "Test\\ with backslash","nextfield",NULL,NULL,NULL,NULL,NULL,NULL } },
         { "Test with \\\" escaped quote,nextfield", 2, { "Test with \" escaped quote","nextfield",NULL,NULL,NULL,NULL,NULL,NULL } },
         { "Test with \"\" escaped quote,nextfield", 2, { "Test with \" escaped quote","nextfield",NULL,NULL,NULL,NULL,NULL,NULL } },
+        { "\"Test (quoted) with \"\" escaped quote\",\"nextfield\"", 2, { "Test (quoted) with \" escaped quote","nextfield",NULL,NULL,NULL,NULL,NULL,NULL } },
         { "\"Unescaped quote test\",nextfield", 2, { "Unescaped quote test","nextfield",NULL,NULL,NULL,NULL,NULL,NULL } },
         { NULL, 0, { NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL } },
 };