applypatch: Fix a memory leak in ApplyImagePatch().

$ valgrind --leak-check=full out/host/linux-x86/nativetest64/recovery_host_test/recovery_host_test

==36755== 112 bytes in 1 blocks are definitely lost in loss record 4 of 16
==36755==    at 0x40307C4: malloc (valgrind/coregrind/m_replacemalloc/vg_replace_malloc.c:270)
==36755==    by 0x40C1669: operator new(unsigned long) (external/libcxxabi/src/cxa_new_delete.cpp:46)
==36755==    by 0x18D6A8: ApplyImagePatch(unsigned char const*, unsigned long, Value const*, std::__1::function<unsigned long (unsigned char const*, unsigned long)>, sha_state_st*, Value const*) (bootable/recovery/applypatch/imgpatch.cpp:62)
==36755==    by 0x18D02B: ApplyImagePatch(unsigned char const*, unsigned long, unsigned char const*, unsigned long, std::__1::function<unsigned long (unsigned char const*, unsigned long)>) (bootable/recovery/applypatch/imgpatch.cpp:134)
==36755==    by 0x160D15: GenerateTarget(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >*) (bootable/recovery/tests/component/imgdiff_test.cpp:85)
==36755==    by 0x11FA7D: verify_patched_image(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&) (bootable/recovery/tests/component/imgdiff_test.cpp:96)
==36755==    by 0x12966C: ImgdiffTest_zip_mode_smoke_trailer_zeros_Test::TestBody() (bootable/recovery/tests/component/imgdiff_test.cpp:295)
==36755==    by 0x235EF9: testing::Test::Run() (external/googletest/googletest/src/gtest.cc:2455)
==36755==    by 0x236CBF: testing::TestInfo::Run() (external/googletest/googletest/src/gtest.cc:2653)
==36755==    by 0x2372D6: testing::TestCase::Run() (external/googletest/googletest/src/gtest.cc:2771)
==36755==    by 0x23EEE6: testing::internal::UnitTestImpl::RunAllTests() (external/googletest/googletest/src/gtest.cc:4648)
==36755==    by 0x23EB45: testing::UnitTest::Run() (external/googletest/googletest/src/gtest.cc:2455)

std::unique_ptr<z_stream, decltype(&deflateEnd)> strm(new z_stream(), deflateEnd);

Only the internally allocated buffers inside 'strm' would be free'd by
deflateEnd(), but not 'strm' itself.

This CL fixes the issue by moving 'strm' to stack variable. Note that we
only need to call deflateEnd() on successful return of deflateInit2().

Test: recovery_host_test && recovery_component_test
Change-Id: I39b9bdf62376b8029f95cab82c8542bfcb874009