Fix static analyzer complaints

frameworks/base/core/jni/android_view_MotionEvent.cpp:383:12: warning:
Potential leak of memory pointed to by 'event'

frameworks/base/core/jni/AndroidRuntime.cpp:975:20: warning: Null passed
to a callee that requires a non-null 1st parameter

For the former, it was surprising to me that the analyzer couldn't
figure out that `event == nativePtr` for the latter check. Filed
https://bugs.llvm.org/show_bug.cgi?id=33540 upstream about it.

For the latter, it was complaining because `className` could be NULL
(more precisely, we have a NULL check at the top of the function it's
declared in, so NULL is presumably a valid value).

Bug: None
Test: Ran mma; complaints are gone.
Change-Id: I26a91ae25934f95acbfdbe4f3641e081fbc66c6d