fixed-bit.c (SATFRACT): Only declare / set min_low, min_high if TO_MODE_UNSIGNED == 0.

	* fixed-bit.c (SATFRACT) <FROM_TYPE=1, TO_TYPE=4>: Only
	declare / set min_low, min_high if TO_MODE_UNSIGNED == 0.
	(SATFRACT) <FROM_TYPE=TO_TYPE=4>: Only declare / set min_low,
	min_high if FROM_MODE_UNSIGNED == 0 and TO_MODE_UNSIGNED == 0.

From-SVN: r195141