pidfile: Always initialize global variables

Always initialize global variables, even though they cannot be used in
current code paths without being initialized at runtime.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

pidfile.c

@@ -42,7 +42,7 @@
 
 #ifndef pidfile
 static char *pidfile_path = NULL;
-static pid_t pidfile_pid;
+static pid_t pidfile_pid  = 0;
 
 static void pidfile_cleanup(void);