cmdutil: pass node instead of ctx to diffordiffstat 93bcc73df8d5 changed showpatch to use ctx's more, but it accidentally passed prev as a context and node as a binary string, when both should be passed as binary strings (since diffordiffstat tries to resolve them via repo[X]). This affected hggit since the existing ctx belongs to the git overlay, but the resolved context (from the repo[X] resolution) should belong to the main repo. This broke a test because it tried to look in the git repo for data that didn't exist. This feels like a deeper issue in hggit somewhere, but the fix is here trivial and obviously more correct