Core: LowLevelHttpResponse not disconnected when HttpResponse construction throws RuntimeException #2177

Environment details:

1. Core — HttpRequest.execute() in google-http-client
2. OS type and version: Any (not OS-specific)
3. Java version: Any (reproduces on Java 8+)
4. google-http-client version(s): reproducible on current main

Steps to reproduce:

1. Implement a LowLevelHttpResponse whose getContentEncoding() throws a RuntimeException.
2. Execute an HttpRequest against that transport.
3. Catch the RuntimeException from execute().
4. Observe disconnect() was never called on the low-level response.

Code example:

MockLowLevelHttpResponse failingResponse = new MockLowLevelHttpResponse() {
  @Override
  public String getContentEncoding() {
    throw new RuntimeException("simulated failure");
  }
};

HttpTransport transport = new MockHttpTransport() {
  @Override
  public LowLevelHttpRequest buildRequest(String method, String url) throws IOException {
    return new MockLowLevelHttpRequest().setResponse(failingResponse);
  }
};

HttpRequest req = transport.createRequestFactory()
    .buildGetRequest(new GenericUrl("http://example.com"));

try {
  req.execute();
} catch (RuntimeException e) {
  // failingResponse.isDisconnected() == false  <-- BUG: socket leaked
}

Stack trace:
None — silent resource leak, not a crash. The RuntimeException propagates as expected; the
bug is that execute()'s finally block never calls LowLevelHttpResponse#disconnect() here.

External references:

• HttpRequest#execute(): google-http-client/src/main/java/com/google/api/client/http/HttpRequest.java

Any additional information:
Under sustained error conditions, leaked connections accumulate until the pool is exhausted,
risking DoS/thread starvation. Pre-existing bug, unrelated to security hardening — found
opportunistically during a security audit of this file.

Proposed fix — in execute()'s finally block, add a guarded disconnect():

} finally {
  if (!responseConstructed && lowLevelHttpResponse != null) {
    try {
      InputStream c = lowLevelHttpResponse.getContent();
      if (c != null) c.close();
    } catch (IOException ignored) {}
    try {
      lowLevelHttpResponse.disconnect();
    } catch (IOException ignored) {}
  }
}

Regression test testExecute_disconnectOnResponseConstructionFailure included in the
accompanying PR.