fix: xterm copy-out logic is erratic with line wrapping

[starpit]

when capturing the output of the pty, line wrapping causes odd behavior, with lines squashed together strangely

this might be due to some webpack or typescript behavior for variables declared but never defined before first use? we were assuming it was undefined, but... this doesn't appear to be the case? in any case, we shouldn't be using variables with no defined value.

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