Remove usage of find_thread when calling resume_status_pending_p
    
    Replace with find_thread.  Instead of setting the flag in the callback,
    make the callback return true/false, and check the result against NULL
    in the caller.
    
    gdb/gdbserver/ChangeLog:
    
    	* linux-low.c (resume_status_pending_p): Return bool, remove
    	flag_p argument.
    	(linux_resume): Use find_thread.