v.util: improve find_diff_cmd: don't add spaces to result without env…

… opts (#21242)

vlib/v/util/diff/diff.v

@@ -40,11 +40,11 @@ pub fn find_working_diff_command() !string {
 				}
 			}
 			if diffcmd in ['code', 'code.cmd'] {
-				// there is no guarantee that the env opts exist
-				// or include `-d`, so (harmlessly) add it
+				// Make sure the diff flag `-d` is included in any case.
 				return '${diffcmd} ${env_diffopts} -d'
 			}
-			return '${diffcmd} ${env_diffopts}'
+			// Don't add spaces to the cmd if there are no `env_diffopts`.
+			return if env_diffopts != '' { '${diffcmd} ${env_diffopts}' } else { diffcmd }
 		}
 	}
 	return error('No working "diff" command found')