Merge bitcoin/bitcoin#22279: fuzz: add missing ECCVerifyHandle to base_encode_decode

906d791 fuzz: add missing ECCVerifyHandle to base_encode_decode (Andrew Poelstra)

Pull request description:

  It is possible to trigger a fuzztest failure in the `base_encode_decode` by asking it to decode any PSBT that has HD keypaths in it. For example, this one

  ```
  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
  ```

  which I took straight from the PSBT test vectors. The reason is that in src/psbt.h we call `DeserializeHDKeypaths`, which in turn calls `CPubKey::IsFullyValid`, which in turn asserts that a secp context has been created.

  The error appears to be masked on many systems by the definition of `instance_of_eccryptoclosure` in src/script/bitcoinconsensus.cpp, which defines a static object which contains an `ECCVerifyHandle`. If you just comment out that line you can reliably trigger the fuzz test failure, e.g. by creating a file `crash` with the above PSBT, and runnnig

  ```
  ASAN_OPTIONS=symbolize=0:detect_stack_use_after_return=1:check_initialization_order=1:strict_init_order=1 UBSAN_OPTIONS=suppressions=./test/sanitizer_suppressions/ubsan:print_stacktrace=1:halt_on_error=1:report_error_type=1 FUZZ=base_encode_decode ./src/test/fuzz/fuzz -seed_inputs=crash
  ```

ACKs for top commit:
  practicalswift:
    cr ACK 906d791

Tree-SHA512: b98b60573c21efe28503fe351883c6f0d9ac99d0dd6f100537b16ac53476617b8a3f899faf0c23d893d34a01b3bbe4a784499ec6f9c7000292e850bed449bd85

Author: MarcoFalke

src/test/fuzz/base_encode_decode.cpp

@@ -14,7 +14,12 @@
 #include <string>
 #include <vector>
 
-FUZZ_TARGET(base_encode_decode)
+void initialize_base_encode_decode()
+{
+    static const ECCVerifyHandle verify_handle;
+}
+
+FUZZ_TARGET_INIT(base_encode_decode, initialize_base_encode_decode)
 {
     const std::string random_encoded_string(buffer.begin(), buffer.end());