Merge #18426: scripts: previous_release: improve behaviour on failed download

332f373a9d [scripts] previous_release: improve failed download error message (Sebastian Falbesoner)

Pull request description:

  Currently, if the earlier release build/fetch script `previous_release.sh` is invoked with the option `-b` (intending to fetch a binary package from `https://bitcoin.org`) and the download fails, the user sees the following confusing output:
  ```
  $ contrib/devtools/previous_release.sh -r -b v0.9.5
  [...]
  gzip: stdin: not in gzip format
  tar: Child returned status 1
  tar: Error is not recoverable: exiting now
  ```
  This implies that the download worked, but the archive is corrupted, when in reality the HTML document containing the delivery fail reason (most likely 404 Not Found) is saved and tried to get unpacked. In contrast to wget, curl is a bit stubborn and needs explicit instructions to react to server errors via the flag `-f` (outputs error message and returns error code, ideal for scripts): https://curl.haxx.se/docs/manpage.html#-f

  On the PR branch, the output on failed download looks now the following:
  ```
  $ contrib/devtools/previous_release.sh -r -b v0.9.5
  [...]
  curl: (22) The requested URL returned error: 404 Not Found
  Download failed.
  ```

ACKs for top commit:
  fanquake:
    ACK 332f373a9d

Tree-SHA512: 046c931ad9e78aeb2d13faa4866d46122ed325aa142483547c2b04032d03223ed2411783b00106fcab0cd91b2f78691531ac526ed7bb3ed7547b6e2adbfb2e93

contrib/devtools/previous_release.sh

@@ -139,7 +139,10 @@ pushd "$TARGET" || exit 1
         fi
         URL="https://bitcoin.org/$BIN_PATH/bitcoin-${tag:1}-$PLATFORM.tar.gz"
         echo "Fetching: $URL"
-        curl -O $URL
+        if ! curl -O -f $URL; then
+            echo "Download failed."
+            exit 1
+        fi
         tar -zxf "bitcoin-${tag:1}-$PLATFORM.tar.gz" -C "$tag" --strip-components=1 "bitcoin-${tag:1}"
         rm "bitcoin-${tag:1}-$PLATFORM.tar.gz"
       fi