Original vmlinux_path__exit() doesn't revert vmlinux_path__nr_entries to
its original state. After the while loop vmlinux_path__nr_entries
becomes -1 instead of 0.
This makes a problem that, if runs twice, during the second run
vmlinux_path__init() will set vmlinux_path[-1] to strdup("vmlinux"),
corrupts random memory.
This patch reset vmlinux_path__nr_entries to 0 after the while loop.