bugfix: initialize pid (as read from pidfile) to zero

If we didn't read any number from a pid file, we'll return
an unitialized variable to the caller, and it will treat
that garbage as a pid of a process (possible to kill).

Fix that.

lib/pidfile.c

@@ -37,7 +37,7 @@
 pid_t read_pid (char *pidfile)
 {
   FILE *f;
-  long pid;
+  long pid = 0;
 
   if (!(f=fopen(pidfile,"r")))
     return 0;