git-gui: Using "Stage To Commit" does not always stage all selected files.

Hello,

Using "Stage To Commit" in git-gui does not always stage all selected files.

After startup of git-gui the first modified file is automatically selected.
Selecting another file and then using "Stage to Commit" only the second file is actually staged.

It looks like the reason for this is that selected_paths is not set when a file is automatically selected after startup/refresh/scanning.

How to reproduce:
echo >> userdiff.h
echo >> userdiff.c
git gui&
-> userdiff.c is automatically selected
hold Ctrl and select userdiff.h
Ctrl-T
-> only userdiff.h is staged, userdiff.h remains unstaged

Greetings Peter