Balance of subwindows GCU

[Kramborn]

I pulled b1011f7.
But the sub-windows are too small, and there are large spaces between the main window and sub-windows.

I am using -mgcu, 2x2 window configuration, and the terminal size is 150x41.

Following patch works for me, but not sure if it is ok for everyone.

diff --git a/src/main-gcu.c b/src/main-gcu.c
index ebb2b5a..4365c12 100644
--- a/src/main-gcu.c
+++ b/src/main-gcu.c
@@ -403,7 +403,8 @@ static void balance_dimension(int *size, int *start, int term_group_index,
                        if (window_size > min_term0_size + subterm_group_count + *size * subterm_group_count)
                                (*size)++;
                } else {
-                       *size = MIN(min_term0_size, window_size - min_term0_size - comfy_subterm_size - subterm_group_count);
+                       //*size = MIN(min_term0_size, window_size - min_term0_size - comfy_subterm_size - subterm_group_count);
+                       *size = MIN(min_term0_size, window_size - subterm_group_count*(min_term0_size + 1));
                }
                *start = window_size - *size;
        } else {