Bug in plotutils-2.5.1::tek2plot

[Poul-Henning Kamp]

Hi there,

I found a subtle bug in the tek2plot utility of plotutils 2.5.1.

Optimized Tek4014 enhanced 12-bit coordinate sequences are not
correctly parsed if the EB is not included, but LoY is.

The result of this is that short vertical lines risk getting a slant
because the LoY change gets misinterpreted.

Documentation:

        Tektronix 4014 and 4014-1 User's Manual

        Rev B. OCT 1974

        Page F-4:

        The Extra Byte need not be sent, but the Low Order Y
        byte must always be sent if the Extra Byte is sent. The rules
        for Shortened Address Transmission only changes (over
        that of the Standard Terminal as previously mentioned in
        preceding sections) when the Extra Byte changes; then
        send the Extra, Low Y, and Low X bytes

Other Documentation:
        The xterm program parses this correctly.

Sample sequence:

        ^]      GS

        "       HIY     2       
        b       EB      2
        k       LOY     11
        L       LOX     12

        !       HIY     1
        r       LOY     18             
        L       LOX     12            

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