fix(preSampling): make vae/pixels optional on samplerCustomSettings.ip2p (#1029)

The latent-only call site passes neither vae nor pixels, so the IP2P
guider raises TypeError whenever a latent is supplied instead of an
image. samplerFull.ip2p in samplers.py already has the optional form.

py/nodes/preSampling.py

@@ -367,7 +367,7 @@ class samplerCustomSettings:
     FUNCTION = "settings"
     CATEGORY = "EasyUse/PreSampling"
 
-    def ip2p(self, positive, negative, vae, pixels, latent=None):
+    def ip2p(self, positive, negative, vae=None, pixels=None, latent=None):
         if latent is not None:
             concat_latent = latent
         else: