Some collection APIs with nullable return value don't reset `CBLError.code`

[blaugold]

APIs which can return nullptr without it being an error need to set CBLError.code to 0 in this case. CBLCollection_GetDocument does this:

couchbase-lite-C/src/CBLCollection_CAPI.cc

Lines 136 to 139 in 6924256

	auto doc = collection->getDocument(docID).detach();
	if (!doc && outError)
	outError->code = 0;
	return doc;

This is necessary because CBLError is often allocated on the stack once and then reused. If a previous call failed, CBLError.code contains the result code for the previous call.

CBLDatabase_Scope, CBLDatabase_Collection and CBLScope_Collection don't do this. I have not checked all APIs for this, so there might be more instances.

[pasin]

Thanks for reporting this.

[pasin]

CBL-4928