Merge #9937: rpc: Prevent dumpwallet from overwriting files

0cd9273 rpc: Prevent `dumpwallet` from overwriting files (Wladimir J. van der Laan)

Pull request description:

  Prevent arbitrary files from being overwritten by `dumpwallet`. There have been reports that users have overwritten wallet files this way. It may also avoid other security issues.

  Fixes #9934. Adds mention to release notes and adds a test.

Tree-SHA512: 268c98636d40924d793b55a685a0b419bafd834ad369edaec08227ebe26ed4470ddea73008d1c4beb10ea445db1b0bb8e3546ba8fc2d1a411ebd4a0de8ce9120

doc/release-notes.md

@@ -83,6 +83,9 @@ Low-level RPC changes
   * `getwalletinfo`
   * `getmininginfo`
 
+- `dumpwallet` no longer allows overwriting files. This is a security measure
+  as well as prevents dangerous user mistakes.
+
 Credits
 =======