rpnlist: lists are not equal if either has an error

the errors of two lists cannot be compared because the line may have
changed but the error column and length may not have, which resulted in
the error not be displayed correctly; therefore, if either RPN list
being contains an error, the lists are not equal
enable/disable go to error actions when there are errors or not

added new errors available signal from edit box
modified edit box update errors slot to emit new signal
corrected problem with start/end index when there are no errors
connect new signal to go to next/previous error actions
start errors actions disabled
added checks to catch go to error keys when there are no error