Non-matching captures in alternatives cause a UTF-8 Error.

[sixears]

If the regex contains a capture that isn't matched because it's in on a side of an alternation that is not used, a UTF-8 error is caused:

λ> "acd" ?=~ [re|a((b)|(c))d|]
Match {matchSource = "acd", captureNames = fromList [], matchArray = array (CaptureOrdinal {getCaptureOrdinal = 0},CaptureOrdinal {getCaptureOrdinal = 3}) [(CaptureOrdinal {getCaptureOrdinal = 0},Capture {captureSource = "acd", capturedText = "acd", captureOffset = 0, captureLength = 3}),(CaptureOrdinal {getCaptureOrdinal = 1},Capture {captureSource = "acd", capturedText = "c", captureOffset = 1, captureLength = 1}),(CaptureOrdinal {getCaptureOrdinal = 2},*** Exception: utf8_correct_bs: UTF-8 decoding error
CallStack (from HasCallStack):
  error, called at ./Text/RE/ZeInternals/Types/Match.lhs:248:13 in regex-1.1.0.0-Ejn9jxFmirEFrePEa32Cpi:Text.RE.ZeInternals.Types.Match

This also causes a similar error with capturedText, matchCaptures, etc.