osc.lua: cycle tracks when there's only one

When there is 1 audio or sub track, make left click select or unselect
it directly without opening the selector. The script-opt command is
ignored in this case.

Requested by sfan5.

DOCS/man/osc.rst

@@ -497,6 +497,9 @@ Configurable Options
 The following options configure what commands are run when the buttons are
 clicked. ``mbtn_mid`` commands are also triggered with ``shift+mbtn_left``.
 
+When there's only one track of a type, left clicks on track buttons always cycle
+it instead of using the configured command.
+
 ``title_mbtn_left_command=script-binding select/select-playlist; script-message-to osc osc-hide``
 
 ``title_mbtn_mid_command=show-text ${filename}``

player/lua/osc.lua

@@ -1866,7 +1866,9 @@ local function osc_init()
         return ("\238\132\134" .. osc_styles.smallButtonsLlabel .. " " ..
                (mp.get_property_native("aid") or "-") .. "/" .. audio_track_count)
     end
-    ne.eventresponder["mbtn_left_up"] = command_callback(user_opts.audio_track_mbtn_left_command)
+    ne.eventresponder["mbtn_left_up"] = command_callback(audio_track_count == 1
+        and "cycle audio"
+        or user_opts.audio_track_mbtn_left_command)
     ne.eventresponder["shift+mbtn_left_up"] = command_callback(
         user_opts.audio_track_mbtn_mid_command)
     ne.eventresponder["mbtn_right_up"] = command_callback(user_opts.audio_track_mbtn_right_command)
@@ -1886,7 +1888,9 @@ local function osc_init()
         return ("\238\132\135" .. osc_styles.smallButtonsLlabel .. " " ..
                (mp.get_property_native("sid") or "-") .. "/" .. sub_track_count)
     end
-    ne.eventresponder["mbtn_left_up"] = command_callback(user_opts.sub_track_mbtn_left_command)
+    ne.eventresponder["mbtn_left_up"] = command_callback(audio_track_count == 1
+        and "cycle sub"
+        or user_opts.sub_track_mbtn_left_command)
     ne.eventresponder["shift+mbtn_left_up"] = command_callback(user_opts.sub_track_mbtn_mid_command)
     ne.eventresponder["mbtn_right_up"] = command_callback(user_opts.sub_track_mbtn_right_command)