[binutils-gdb] Correctly notice empty sysroots in solib_find_1

[sergiodj+buildbot at redhat dot com]

*** TEST RESULTS FOR COMMIT f8773be1be076f828b93ac3bebeab3f782e191e4 ***

Author: Gary Benson <gbenson@redhat.com>
Branch: master
Commit: f8773be1be076f828b93ac3bebeab3f782e191e4

Correctly notice empty sysroots in solib_find_1
Some parts of solib_find_1 should only operate if the sysroot
is nonempty after processing, but the logic that checked this
happened before trailing slashes were stripped so empty but
non-NULL sysroots were possible.  This commit moves the logic
so it correctly notices all empty sysroots.

gdb/ChangeLog:

	* solib.c (solib_find_1): Set local variable sysroot to NULL if
	it is the empty string after trailing slashes have been stripped.