Use push_empty_string()

Rev: src/builtin.cmod:1.178
Rev: src/language.yacc:1.358
Rev: src/modules/HTTPLoop/requestobject.c:1.30
Rev: src/modules/Image/encodings/iff.c:1.16
Rev: src/modules/Image/encodings/ras.c:1.25
Rev: src/modules/Image/encodings/xwd.c:1.29
Rev: src/modules/Image/font.c:1.85
Rev: src/modules/Mysql/mysql.c:1.90
Rev: src/modules/Odbc/odbc.c:1.38
Rev: src/modules/Odbc/odbc_result.c:1.40
Rev: src/modules/_Image_GIF/image_gif.c:1.22
Rev: src/modules/_Roxen/roxen.c:1.45
Rev: src/modules/files/efuns.c:1.164
Rev: src/modules/files/file.c:1.350
Rev: src/modules/spider/spider.c:1.130
Rev: src/modules/spider/xml.c:1.74
Rev: src/modules/system/memory.c:1.33
Rev: src/modules/system/passwords.c:1.47