sanei_thread: Corrected some additional mistakes.

Major review and check is required followed by some extensive testing.
We might also go for a different solution yet but we will see.

include/sane/sanei_thread.h

@@ -141,7 +141,7 @@ extern SANE_Bool sanei_thread_is_valid (SANE_Pid pid);
  *  For details on the pthread_t type, see in particular Issue 6 of
  *  http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/sys_types.h.html
  */
-#define sanei_thread_invalidate(sane_pid) ((sane_pid).pid = SANE_FALSE)
+#define sanei_thread_invalidate(sane_pid) ((sane_pid).is_valid = SANE_FALSE)
 
 /** Initialize a SANE_Pid
  *

sanei/sanei_thread.c

@@ -117,7 +117,7 @@ sanei_thread_is_forked( void )
 static void
 sanei_thread_set_invalid( SANE_Pid *pid )
 {
-  pid->is_valid = SANE_FALSE;
+	sanei_thread_invalidate(*pid);
 }
 #endif