82c3b3f8e0 Remove sharp edge (uninitialized m_filter_type) when using the compiler-generated constructor for BlockFilter (practicalswift)
Pull request description:
Remove sharp edge (uninitialised member `m_filter_type`) when using the compiler-generated constructor for `BlockFilter`.
Before (but after added test):
```
$ src/test/test_bitcoin -t blockfilter_tests/blockfilter_basic_test
Running 1 test case...
test/blockfilter_tests.cpp(118): error: in "blockfilter_tests/blockfilter_basic_test": check default_ctor_block_filter_1.GetFilterType() == default_ctor_block_filter_2.GetFilterType() has failed [ != ]
*** 1 failure is detected in the test module "Bitcoin Test Suite"
```
After:
```
$ src/test/test_bitcoin -t blockfilter_tests/blockfilter_basic_test
Running 1 test case...
*** No errors detected
```
Tree-SHA512: 21d41f036b0bf12adcf1a788d84747353f2023cb85fd8ea6c97222967032e8bf54e7910cadb45dfcecd78e5b5dca86685f78cad0596b6d1a08f910ebf20d90aa