set tag PRE-EMPHASIS=yes when FLAGS PRE is present in cue

[00blt00]

According to https://hydrogenaud.io/index.php/topic,99394.0.html it would be very nice to have ability of setting tag PRE-EMPHASIS=yes if FLAGS PRE exists in source CUE. Currently FLAGS PRE clause is properly copied to destination CUE but since CUE files are not used in foobar2000 properly, some can't be processed at all, PRE-EMPHASIS tag is the only option which is already interpreted by dsp and/or postprocessing de-emphasis plugin.