Fix ldbl-128 j0l spurious underflows (bug 19156).

My recent addition of more tests for j0 showed up that the ldbl-128
implementation of j0l produces spurious underflow exceptions for
arguments close to 0 (when the result is very close to 1).  This patch
fixes this by just returning the argument in that case.

Tested for mips64 (where it fixes the recently-added tests that were
previously failing).

	[BZ #19156]
	* sysdeps/ieee754/ldbl-128/e_j0l.c (__ieee754_j0l): Return 1 for
	arguments very close to 0.