Fix bug reported by DigitalMan

It looks like this has been a long-standing UIFC bug (pre-3.0)

If a uifc list that can scroll is showing the bottom-most line,
and an option that is not the last is deleted, and both *cur and
*bar are left untouched, *bar would be adjusted to be too high,
resulting in various highlight bar corruption issues.

This commit just rewrites that logic to be comprehensible, and
ensures that if bar is set such that the list would end before the
bottom of the window, it gets moved up.  This makes delete do the
right thing (didn't test with insert, that may do weird things).

Also, since I figured out a good definition of what bar actually
represtens, add a comment to that effect.

src/uifc/uifc32.c

@@ -643,6 +643,9 @@ static inline char* non_null_str(char* str) { return str == NULL ? "" : str; }
 /****************************************************************************/
 /* General menu function, see uifc.h for details.							*/
 /****************************************************************************/
+// cur is the currently selected option.
+// bar is how many unselected options are displayed up to (ie: The number
+//     of unselected options before cur currently displayed on screen)
 int ulist(uifc_winmode_t mode, int left, int top, int width, int *cur, int *bar
 	, const char *initial_title, char **option)
 {
@@ -974,16 +977,24 @@ int ulist(uifc_winmode_t mode, int left, int top, int width, int *cur, int *bar
 				(*bar)=opts-1;
 			if((*bar)<0)
 				(*bar)=0;
+			// Set i to the first option to display on the screen...
 			i=(*cur)-(*bar);
+			// If bar is too high, start with first item
 			if (i < 0) {
-				*bar += i;
+				*bar = *cur;
 				i = 0;
 			}
-			if(i+(height-vbrdrsize-1)>=opts) {
-				(*bar)=(height-vbrdrsize);
+			// If the number of options on screen is greater than the rows on screen...
+			if ((opts - i) > (height - vbrdrsize)) {
+				*bar = height - vbrdrsize;
 				if (*bar > *cur)
 					*bar = *cur;
-				i=(*cur)-(*bar)+1;
+				i=(*cur)-(*bar);
+			}
+			// If there are enough options to fill the screen, but the screen is not filled...
+			if ((opts > (height - vbrdrsize)) && ((opts - i) < (height - vbrdrsize))) {
+				*bar += (height - vbrdrsize) - (opts - i);
+				i=(*cur)-(*bar);
 			}
 		}
 		if((*cur)<0)