When using the "copy commit message to clipboard" action, the message will end
up in the clipboard with duplicate line breaks. The same issue also affects the
"Reword Commit" command. GetCommitMessage(), the function used to retrieve the
commit message first splits the output returned by git into separate lines -
without removing the line breaks. After removing the first line (which contains
the commit SHA), it joins the lines of the message itself back together - adding
a second set of line breaks along the way. Stop this from happening.
Fixes#1808.
