internal/number: enable the fast case more often
internal/number: enable the fast case more often

Change-Id: I0849b029eee7b233f4c6f676d7bbdde3820c63e4
Reviewed-on: https://go-review.googlesource.com/46470
Run-TryBot: Marcel van Lohuizen <a22d082192f3ccf984644a4f482781f4c2d65180@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Nigel Tao <58ae08b3356928ff9c67562b4719487d54fe8348@golang.org>

golang/text