validate: make clippy happy

warning: redundant else block
   --> src/cmd/validate.rs:273:28
    |
273 |                       } else {
    |  ____________________________^
274 | |                         return fail_clierror!("Header Validation error: {e}.");
275 | |                     }
    | |_____________________^
    |
    = help: remove the `else` block and move the contents out
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#redundant_else
    = note: `-W clippy::redundant-else` implied by `-W clippy::pedantic`

[skip ci]

src/cmd/validate.rs

@@ -270,9 +270,9 @@ pub fn run(argv: &[&str]) -> CliResult<()> {
                              You may also want to transcode your data to UTF-8 first using `iconv` \
                              or `recode`."
                         );
-                    } else {
-                        return fail_clierror!("Header Validation error: {e}.");
                     }
+                    // its not a UTF-8 error, report a generic header validation error
+                    return fail_clierror!("Header Validation error: {e}.");
                 },
             }
         }