first letter is not inserted in python omnifunc

[p00f]

When I use the builtin python omnifunc, the first letter of the selection is not inserted:

cmp.mp4

[liskin]

This is almost certainly caused by hrsh7th/nvim-cmp#1177, because python omnifunc produces a textEdit that keeps the "a" unchanged and simply appends "rgv", but get_replace_range discards that range and invents its own that replaces the "a" as well. What seems to help is to configure mappings to always insert rather than replacing (so that get_replace_range is never invoked).