Fixed bug #570

SDL_SemWaitTimeout in src/thread/generic/SDL_syssem.c line 179 (SVN trunk):

--sem->count;

should be

if (retval == 0) {
    --sem->count;
}

Without this, sem->count will underflow on timeout effectively breaking the
semaphore. It appears that the implementation has been wrong since the initial
revision.

--HG--
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%403844

src/thread/generic/SDL_syssem.c

@@ -176,7 +176,9 @@ SDL_SemWaitTimeout(SDL_sem * sem, Uint32 timeout)
                                      sem->count_lock, timeout);
     }
     --sem->waiters_count;
-    --sem->count;
+    if (retval == 0) {
+        --sem->count;
+    }
     SDL_UnlockMutex(sem->count_lock);
 
     return retval;