kconfig: fix segfault when detecting recursive dependency

Following sample Kconfig generated a segfault:

config FOO
        bool
        select PERF_EVENTS if HAVE_HW_BREAKPOINT

config PERF_EVENTS
        bool

config HAVE_HW_BREAKPOINT
        bool
        depends on PERF_EVENTS

Fix by reverting back to a valid property if there was no
property on the stack of symbols.

The above pattern were seen in sh Kconfig.
A fix for the Kconfig file has been sent to the sh folks.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Michal Marek <mmarek@suse.cz>