cpp: Allow changing the error of a result

* lang/cpp/src/result.h (class Result): Add member function setError.
--

This can be used to replace the error of a result with a more suitable
error.

GnuPG-bug-id: 5939

NEWS

@@ -11,6 +11,7 @@ Noteworthy changes in version 1.17.2 (unreleased)
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  cpp: RevocationReason                      NEW.
  cpp: GpgRevokeKeyEditInteractor            NEW.
+ cpp: Result::setError                      NEW.
  qt: RevokeKeyJob                           NEW.
  qt: Protocol::revokeKeyJob                 NEW.
 

lang/cpp/src/result.h

@@ -50,6 +50,14 @@ public:
     {
         return mError;
     }
+    /**
+     * Replaces the error set during construction with \p error.
+     * Use with care, e.g. to set a more suitable error.
+     */
+    void setError(const Error &error)
+    {
+        mError = error;
+    }
 
 protected:
     Error mError;