virpcimock: Initialize real_close before using it

real_close() is not inialized by the first invocation of close(). That
causes an issue when the mock is used before others and a call of
real_close() results in a jump to NULL pointer.

Signed-off-by: Roman Bolshakov <r.bolshakov@yadro.com>
Reviewed-by: Andrea Bolognani <abologna@redhat.com>

tests/virpcimock.c

@@ -1123,6 +1123,8 @@ opendir(const char *path)
 int
 close(int fd)
 {
+    init_syms();
+
     if (remove_fd(fd) < 0)
         return -1;
     return real_close(fd);