If Number of Scan Lines (R9) is changed with a value less than the current VLC, then:
* on CRTCs 0/1/2, VLC overflows and will count up to its maximum value (31) before looping back and counting up again until it reaches the new value of R9
* on CRTCs 3/4, the current line is considered the last one of this CRTC character and VLC will change reset to 0 on the next line
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