Fix close abort

[ttytm]

Fixes #439

Current issue repro in a neogit status buffer:

• ca in the status buffer to amend to the last commit.
• Change something in the commit message - don't save the buffer.
• q to close, a confirmation dialog starts. Hit no in the saves changes confirmation dialog to not confirm the changes.
• The commit is made anyway / See the commit sha changing.

Ref.: #441 (comment)

With the changes in the PR the commit is not being made when not confirming the changes.

The changes are based on the abort implementation:

neogit/lua/neogit/buffers/commit_editor/init.lua

Lines 97 to 102 in a6a7ec0

	[mapping["Abort"]] = function(buffer)
	aborted = true
	buffer:write()
	buffer:close(true)
	end,
	},