Minor planner bugs

[Martin Měřinský]

Hi.
I have found a few minor bugs in 4.5.0 planner. I mentioned it in
"Proposal on new planner layout" thread, but was asked to send it
separately.

Start Subsurface (no log file).
Ctrl+l (Log -> Plan dive).
I get warning "Too many gas mixes".
Warning text is there twice.
It doesn't make sense, because I have nothing in Available gases.

Close the warning.
Hit plus button, to add gas.
I get warning "Too many gas mixes" again.

When going to plan dive, there is automatically one dive planner point,
but no gas. I would suppose to have one gas as well.

Last Dive planner point cannot be removed. The trash icon is stroked
out. Last available gas (once added) cannot be removed neither, but its
icon is not stroked out. In fact, if I add multiple gases, none of them
can be deleted.

Best regards. Martin M.