bpo-38532: Add missing decrefs in PyCFuncPtr_FromDll() (GH-16857)

diff --git a/Modules/_ctypes/_ctypes.c b/Modules/_ctypes/_ctypes.c
index d38d892..93af497 100644
--- a/Modules/_ctypes/_ctypes.c
+++ b/Modules/_ctypes/_ctypes.c
@@ -3554,10 +3554,12 @@
     if (PySys_Audit("ctypes.dlsym",
                     ((uintptr_t)name & ~0xFFFF) ? "Os" : "On",
                     dll, name) < 0) {
+        Py_DECREF(ftuple);
         return NULL;
     }
 #else
     if (PySys_Audit("ctypes.dlsym", "Os", dll, name) < 0) {
+        Py_DECREF(ftuple);
         return NULL;
     }
 #endif