* fix(http): handle invalid gzip stream errors
Explain:
- problem: ReadUrlAsStream could panic when a response claimed gzip encoding but the body was not a valid gzip stream.
- root cause: the gzip reader error was ignored and a nil reader was deferred and read from.
- fix: return the gzip.NewReader error before registering Close or reading.
- validation: go test ./weed/util/http -run TestReadUrlAsStreamReturnsGzipReaderError -count=1; git diff --check.
* test: avoid closing shared global HTTP client in unit test