[binutils-gdb/gdb-7.9-branch] Fix undefined behavior in TUI's TAB expansion

[sergiodj+buildbot@redhat.com]

*** TEST RESULTS FOR COMMIT 4fa4c2f7bed85f7cb116466d3cf194cdb6271c60 ***

Author: Eli Zaretskii <eliz@gnu.org>
Branch: gdb-7.9-branch
Commit: 4fa4c2f7bed85f7cb116466d3cf194cdb6271c60

Fix undefined behavior in TUI's TAB expansion
gdb/ChangeLog:

	* tui/tui-io.c (tui_expand_tabs): Reinitialize the column counter
	before the second loop, to avoid undefined behavior.  Reported by
	Anton Blanchard <anton@samba.org>.

(cherry picked from commit b1a0f704950296b2363192ba91999eef3635700f)