screen: don't die when the window is narrower than four columns

This fixes https://savannah.gnu.org/bugs/?48520.

src/nano.c

@@ -692,9 +692,11 @@ void die_save_file(const char *die_filename, struct stat *die_stat)
 /* Initialize the three window portions nano uses. */
 void window_init(void)
 {
-    /* If the screen height is too small, get out. */
+    /* Compute how many lines the edit subwindow will have. */
     editwinrows = LINES - TOP_ROWS - BOTTOM_ROWS;
-    if (COLS < MIN_EDITOR_COLS || editwinrows < MIN_EDITOR_ROWS)
+
+    /* If there is no room to show anything, give up. */
+    if (editwinrows <= 0)
 	die(_("Window size is too small for nano...\n"));
 
 #ifndef DISABLE_WRAPJUSTIFY

src/nano.h

@@ -576,11 +576,6 @@ enum
 /* The maximum number of entries displayed in the main shortcut list. */
 #define MAIN_VISIBLE (((COLS + 40) / 20) * 2)
 
-/* The minimum editor window columns and rows required for nano to work
- * correctly.  Don't make these smaller than 4 and 1. */
-#define MIN_EDITOR_COLS 4
-#define MIN_EDITOR_ROWS 1
-
 /* The default number of characters from the end of the line where
  * wrapping occurs. */
 #define CHARS_FROM_EOL 8

src/winio.c

@@ -2048,12 +2048,13 @@ void bottombars(int menu)
 	    slen = MAIN_VISIBLE;
     }
 
-    /* There will be this many characters per column, except for the
-     * last two, which will be longer by (COLS % colwidth) columns so as
-     * to not waste space.  We need at least three columns to display
-     * anything properly. */
+    /* Compute the width of each keyname-plus-explanation pair. */
     colwidth = COLS / ((slen / 2) + (slen % 2));
 
+    /* If there is no room, don't print anything. */
+    if (colwidth == 0)
+	return;
+
     blank_bottombars();
 
 #ifdef DEBUG