split_v command only works when there is at least one tmux session already created

[kevinmarquesp]

For some reason, the split_v command only works if there is another tmux session already running:

Look here's an demonstration, take a look at the line 17 of the script, I expect that the next window will use 30% of the height, but it uses more than that a less than the 50% for some reason:

Now I will kill that session in the middle terminal, then I'll create that again:

[vendamere]

This might be similar to #97 (comment)