Remove more OOM error handling code

From the functions:

 - ExpandBufnames
 - buf_modname()
 - do_autocmd_event()
 - ff_create_stack_element()
 - ff_get_visited_list()
 - ins_complete()
 - msg_show_console_dialog()
 - prt_find_resource()
 - vim_findfile_init()

TODO: refactor msg_show_console_dialog() to make sure it doesn't ever return
NULL.

src/hardcopy.c

@@ -1596,8 +1596,6 @@ static int prt_find_resource(char *name, struct prt_ps_resource_S *resource)
   int retval;
 
   buffer = alloc(MAXPATHL + 1);
-  if (buffer == NULL)
-    return FALSE;
 
   vim_strncpy(resource->name, (char_u *)name, 63);
   /* Look for named resource file in runtimepath */