[Bug report]内嵌字幕和外挂字幕来回切换2次之后，外挂字幕不展示

[zdw19840929]

大佬，我发现一个问题，就是外挂字幕和内嵌字幕来回切换2次之后再切换外挂字幕就不展示了，这个是log

[IJKMEDIA][hevc @ 0x109e47350] nal_unit_type: 1(TRAIL_R), nuh_layer_id: 0, temporal_id: 0
[IJKMEDIA][hevc @ 0x109e47350] Output frame with POC 107.
[IJKMEDIA][hevc @ 0x10a8bfbc0] nal_unit_type: 1(TRAIL_R), nuh_layer_id: 0, temporal_id: 0
[IJKMEDIA][hevc @ 0x10a8bfbc0] Output frame with POC 108.
[IJKMEDIA][hevc @ 0x10a8c7b30] nal_unit_type: 0(TRAIL_N), nuh_layer_id: 0, temporal_id: 0
[IJKMEDIA][hevc @ 0x10a8c7b30] Output frame with POC 109.
buffer__________________ 1676.124 1684.548
[IJKMEDIA][hevc @ 0x10a8cfaa0] nal_unit_type: 0(TRAIL_N), nuh_layer_id: 0, temporal_id: 0
[IJKMEDIA][hevc @ 0x10a8cfaa0] Output frame with POC 110.
[IJKMEDIA][hevc @ 0x10a8d7a10] nal_unit_type: 0(TRAIL_N), nuh_layer_id: 0, temporal_id: 0
[IJKMEDIA][hevc @ 0x10a8d7a10] Output frame with POC 111.
[IJKMEDIA][hevc @ 0x10a8df980] nal_unit_type: 0(TRAIL_N), nuh_layer_id: 0, temporal_id: 0
[IJKMEDIA][hevc @ 0x10a8df980] Output frame with POC 112.
[IJKMEDIA][hevc @ 0x10a8afeb0] nal_unit_type: 1(TRAIL_R), nuh_layer_id: 0, temporal_id: 0
[IJKMEDIA][hevc @ 0x10a8afeb0] Output frame with POC 113.
[IJKMEDIA][hevc @ 0x109e47350] nal_unit_type: 1(TRAIL_R), nuh_layer_id: 0, temporal_id: 0
[IJKMEDIA][hevc @ 0x109e47350] Output frame with POC 114.
[IJKMEDIA][hevc @ 0x10a8bfbc0] nal_unit_type: 0(TRAIL_N), nuh_layer_id: 0, temporal_id: 0
[IJKMEDIA][hevc @ 0x10a8bfbc0] Output frame with POC 115.
[IJKMEDIA][hevc @ 0x10a8c7b30] nal_unit_type: 0(TRAIL_N), nuh_layer_id: 0, temporal_id: 0
[IJKMEDIA][hevc @ 0x10a8c7b30] Output frame with POC 116.
[IJKMEDIA][hevc @ 0x10a8cfaa0] nal_unit_type: 0(TRAIL_N), nuh_layer_id: 0, temporal_id: 0
[IJKMEDIA][hevc @ 0x10a8cfaa0] Output frame with POC 117.
[IJKMEDIA][hevc @ 0x10a8d7a10] nal_unit_type: 0(TRAIL_N), nuh_layer_id: 0, temporal_id: 0
[IJKMEDIA][hevc @ 0x10a8d7a10] Output frame with POC 118.
[IJKMEDIA][hevc @ 0x10a8df980] nal_unit_type: 0(TRAIL_N), nuh_layer_id: 0, temporal_id: 0
[IJKMEDIA][hevc @ 0x10a8df980] Output frame with POC 119.
[IJKMEDIA]ijkmp_set_external_subtitle(此处是字幕URL)
[IJKMEDIA]ijkmp_set_external_subtitle()=1
[IJKMEDIA][hevc @ 0x10a8afeb0] nal_unit_type: 0(TRAIL_N), nuh_layer_id: 0, temporal_id: 0
[IJKMEDIA][hevc @ 0x10a8afeb0] Output frame with POC 120.
[IJKMEDIA][hevc @ 0x109e47350] nal_unit_type: 1(TRAIL_R), nuh_layer_id: 0, temporal_id: 0
[IJKMEDIA][hevc @ 0x109e47350] Output frame with POC 121.
[IJKMEDIA][hevc @ 0x10a8bfbc0] nal_unit_type: 1(TRAIL_R), nuh_layer_id: 0, temporal_id: 0
[IJKMEDIA][hevc @ 0x10a8bfbc0] Output frame with POC 122.
[IJKMEDIA][hevc @ 0x10a8c7b30] nal_unit_type: 0(TRAIL_N), nuh_layer_id: 0, temporal_id: 0