1.x: SafeSubscriber not to call RxJavaHooks before delivering the original error.

[akarnokd]

Before the introduction of RxJavaHooks, the SafeSubscriber._onError called the original error handler with the exception it received which was by default an empty handler. The default RxJavaHooks.onError behavior, however is to signal errors to the uncaught exception handler of the caller thread which leads to unnecessary logging or app crashes even though the error itself is to be handled properly.

This PR restores the SafeSubscriber._onError to skip the RxJavaHooks and call the original handler directy so old tracking code should still get all safe error while newer hooking doesn't get called.

Related: #4332.

[codecov-io]

Current coverage is 84.56% (diff: 100%)

Merging #4641 into 1.x will increase coverage by 0.08%

@@                1.x      #4641   diff @@
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  Files           274        274          
  Lines         17766      17766          
  Methods           0          0          
  Messages          0          0          
  Branches       2727       2727          
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+ Hits          15009      15024    +15   
+ Misses         1889       1878    -11   
+ Partials        868        864     -4   

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[akarnokd]

/cc @dlew

[dlew]

LGTM. Thanks for doing this.