Fix python-build's has_broken_mac_readline when Readline is explicitly configured (#3254)

plugins/python-build/bin/python-build

@@ -1585,14 +1585,16 @@ use_freebsd_pkg() {
 has_broken_mac_readline() {
   # Mac OS X 10.4 has broken readline.
   # https://github.com/pyenv/pyenv/issues/23
-  if is_mac && ! configured_with_package_dir "python" "readline/rlconf.h"; then
+  if ! is_mac || configured_with_package_dir "python" "readline/rlconf.h"; then
+    # Not applicable.
+    return 1
+  fi
   if can_use_homebrew; then
     use_homebrew_readline && return 1
   fi
   if can_use_macports; then
     use_macports_readline && return 1
   fi
-  fi
 }
 
 use_homebrew_readline() {