iOS弱网进后台调用pause，buffer加载完成后还会播放

**Describe the bug**
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**To Reproduce**
Steps to reproduce the behavior:
1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

**Expected behavior**
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**Screenshots**
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**Desktop (please complete the following information):**
- OS: [e.g. iOS]
- Browser [e.g. chrome, safari]
- Version [e.g. 22]

**Smartphone (please complete the following information):**
- Device: [e.g. iPhone6]
- OS: [e.g. iOS8.1]
- Browser [e.g. stock browser, safari]
- Version [e.g. 22]

**Additional context**
Add any other context about the problem here.

Start by reproducing the iOS case described in the title: move the player to the background on a weak network, call pause, and wait for buffering to finish. Trace the iOS pause and buffer-completion playback path; the issue is done when playback remains paused after the buffer finishes.

Written by the indexing model from the issue text.