options: make --no-config block all auto-loaded configuration files

Until now, the --no-config was explicitly checked in multiple places to
suppress loading of config files.

Add such a check to the config path code itself, and refuse to resolve
_any_ configuration file locations if the option is set.

osc.lua needs a small fixup, because it didn't handle the situation when
no path was returned. There may some of such cases in the C code too,
but I didn't find any on a quick look.

DOCS/man/en/options.rst

@@ -1412,10 +1412,8 @@ OPTIONS
 ``--no-config``
     Do not load default configuration files. This prevents loading of
     ``~/.mpv/config`` and ``~/.mpv/input.conf``, as well as loading the
-    same files from system wide configuration directories.
-
-    Loading of some configuration files is not affected by this option, such
-    as configuration files for DVB code and fontconfig.
+    same files from system wide configuration directories. Other configuration
+    files are blocked as well, such as resume playback files.
 
     .. note::
 

options/path.c

@@ -32,9 +32,12 @@
 #include <sys/stat.h>
 #include <unistd.h>
 #include <errno.h>
+
 #include "config.h"
+
 #include "common/global.h"
 #include "common/msg.h"
+#include "options/options.h"
 #include "options/path.h"
 #include "talloc.h"
 #include "osdep/io.h"
@@ -53,6 +56,10 @@ static const lookup_fun config_lookup_functions[] = {
 char *mp_find_config_file(void *talloc_ctx, struct mpv_global *global,
                           const char *filename)
 {
+    struct MPOpts *opts = global->opts;
+    if (!opts->load_config)
+        return NULL;
+
     for (int i = 0; config_lookup_functions[i] != NULL; i++) {
         char *path = config_lookup_functions[i](talloc_ctx, global, filename);
         if (!path) continue;
@@ -68,6 +75,10 @@ char *mp_find_config_file(void *talloc_ctx, struct mpv_global *global,
 char *mp_find_user_config_file(void *talloc_ctx, struct mpv_global *global,
                                const char *filename)
 {
+    struct MPOpts *opts = global->opts;
+    if (!opts->load_config)
+        return NULL;
+
     char *homedir = getenv("MPV_HOME");
     char *configdir = NULL;
     char *result = NULL;

player/lua/osc.lua

@@ -121,7 +121,7 @@ function read_config(options, identifier)
 
     local conffilename = "plugin_" .. identifier .. ".conf"
     local conffile = mp.find_config_file(conffilename)
-    local f = io.open(conffile,"r")
+    local f = conffile and io.open(conffile,"r")
     if f == nil then
         -- config not found
     else