softwrap: initialize 'editwincols' early, for computing the number of wraps

When giving a line number on the command line, do_gotolinecolumn() needs
to know the width of the screen to be able to (roughly) place the target
line in the center of the screen.

This fixes https://savannah.gnu.org/bugs/?49462.

src/nano.c

@@ -2560,6 +2560,8 @@ int main(int argc, char **argv)
      * dimensions. */
     window_init();
 
+    editwincols = COLS;
+
     /* Set up the signal handlers. */
     signal_init();