Windows: retry UAC prompt operation in case of failure. This avoids cancel the whole operation if the user is not in front of the machine during UAC prompt (this happens ofter during in-place encryption of big NTFS partitions).

src/Common/Dlgcode.c

@@ -8089,6 +8089,11 @@ int Error (char *stringId, HWND hwnd)
 	return MessageBoxW (hwnd, GetString (stringId), lpszTitle, MB_ICONERROR);
 }
 
+int ErrorRetryCancel (char *stringId, HWND hwnd)
+{
+	if (Silent) return 0;
+	return MessageBoxW (hwnd, GetString (stringId), lpszTitle, MB_ICONERROR | MB_RETRYCANCEL);
+}
 
 int ErrorTopMost (char *stringId, HWND hwnd)
 {