fix clippy lint for constant is_empty check, combine writes

as far as I can tell, it doesn't really hurt to write an empty string if DELIM
is empty. the only reason to check is that the user could modify the config rust
file, and you don't want them to have to modify this code too

blocks/src/main.rs

@@ -118,10 +118,8 @@ impl Block {
                 return String::new();
             }
         };
-        write!(output, "{}", String::from_utf8(out.stdout).unwrap()).unwrap();
-        if !DELIM.is_empty() {
-            write!(output, "{}", DELIM).unwrap();
-        }
+        write!(output, "{}{DELIM}", String::from_utf8(out.stdout).unwrap())
+            .unwrap();
         output
     }
 }