Fix CVTTPS2PI low lane using high lane for lower-bound check - #1068
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Case 0x2C (CVTTPS2PI Gm,Ex) validated GM.sd[0] against EX->f[1] for the negative-overflow test instead of EX->f[0]. The high lane just above correctly tests f[1] twice, and CVTPS2PI just below loops per-lane with f[i]. A low lane in range paired with an out-of-range high lane (e.g. f0=1.0, f1=-3e9) wrongly produced the 0x80000000 indefinite value, and a truly underflowing low lane could slip through. Test the low lane against itself.
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Case 0x2C (CVTTPS2PI Gm,Ex) validated GM.sd[0] against EX->f[1] for the negative-overflow test instead of EX->f[0]. The high lane just above correctly tests f[1] twice, and CVTPS2PI just below loops per-lane with f[i]. A low lane in range paired with an out-of-range high lane (e.g. f0=1.0, f1=-3e9) wrongly produced the 0x80000000 indefinite value, and a truly underflowing low lane could slip through. Test the low lane against itself.