patch 8.0.0299: a window resize is sometimes not taking effect

Problem:    When the GUI window is resized Vim does not always take over the
            new size. (Luchr)
Solution:   Reset new_p_guifont in gui_resize_shell().  Call
            gui_may_resize_shell() in the main loop.

src/main.c

@@ -1118,6 +1118,10 @@ main_loop(
 	    skip_redraw = FALSE;
 	else if (do_redraw || stuff_empty())
 	{
+# ifdef FEAT_GUI
+	    /* If ui_breakcheck() was used a resize may have been postponed. */
+	    gui_may_resize_shell();
+# endif
 #if defined(FEAT_AUTOCMD) || defined(FEAT_CONCEAL)
 	    /* Trigger CursorMoved if the cursor moved. */
 	    if (!finish_op && (