Fix findId spinning if session id is not found.

If session id is not found, the iterator is not incremented
so the end() condition is reached.

The Test:
How is this bug discovered:
Calling AMediaDrm_closeSession() after AMediaDrm_provideKeyResponse()
results in spinning.

This cl is tested on nyc-mr1-dev branch using a NativeClearKeySystemTest
that is not yet checked in. This test will be ported to master soon.
After testing in nyc-mr1-dev, the source in both branches is compared.

Test: ANDROID_BUILD_TOP= ./android-cts/tools/cts-tradefed run cts -m CtsMediaTestCases --test android.media.cts.NativeClearKeySystemTest#testClearKeyPlaybackCenc

bug: 32235473
Change-Id: I58c495d7499f70b7e85cab43911323b143a9d8fd