修复空指针

[guanjianzhe]

我们在fabric后台见到了约700次崩溃，目前版本约覆盖100万用户。只做了简单处理，因为：

1. isFromResumed，isFirstConnect标志并没有真正使用，所有不知道作用是什么；
2. 不想通过保证下载接口的调用时机修复。不应该依赖下载接口的调用时机，保证无空指针。

model.onInfoValid(info) will not be invoked when info is null. Then
model.isFromResumed hasn't been initialized.

log:
Fatal Exception: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.Boolean.booleanValue()' on a null object reference
at com.liulishuo.okdownload.core.listener.assist.Listener1Assist.connectEnd(Listener1Assist.java:88)
at com.liulishuo.okdownload.core.listener.DownloadListener1.connectEnd(DownloadListener1.java:91)

[codecov-io]

Codecov Report

Merging #230 into master will not change coverage.
The diff coverage is 0%.

@@           Coverage Diff           @@
##           master     #230   +/-   ##
=======================================
  Coverage   83.33%   83.33%           
=======================================
  Files          64       64           
  Lines        3828     3828           
  Branches      619      619           
=======================================
  Hits         3190     3190           
  Misses        369      369           
  Partials      269      269

Impacted Files	Coverage Δ
...download/core/listener/assist/Listener1Assist.java	86.88% <0%> (ø)	⬆️

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[rantianhua]

@guanjianzhe Please refine unit test to ensure the test coverage of your changes is > 83%.

[BarretWu]

java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.Boolean.booleanValue()' on a null object reference
at com.liulishuo.okdownload.g.j.d.a.a(Listener1Assist.java:88)
at com.liulishuo.okdownload.g.j.a.a(DownloadListener1.java:91)
at com.liulishuo.okdownload.g.j.c.a(DownloadListenerBunch.java:87)
at com.liulishuo.okdownload.g.f.a$b$i.run(CallbackDispatcher.java:297)
at android.os.Handler.handleCallback(Handler.java:809)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:166)
at android.app.ActivityThread.main(ActivityThread.java:7383)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:469)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:963)