test: a file with no config options, at the end of an %include directory

(The file must contain whitespace or comments to trigger the bug.)

Regression test for 31408.

src/test/conf_examples/include_bug_31408/expected

@@ -0,0 +1,2 @@
+Nickname test31408
+ORPort 31408

src/test/conf_examples/include_bug_31408/included/01_nickname.inc

@@ -0,0 +1 @@
+Nickname test31408

src/test/conf_examples/include_bug_31408/included/02_no_configs.inc

@@ -0,0 +1,3 @@
+# Bug 31048 is triggered when the last file in a config directory:
+#   * contains no configuration options,
+#   * but is non-empty: that is, it contains comments or whitespace.

src/test/conf_examples/include_bug_31408/torrc

@@ -0,0 +1,2 @@
+%include "included"
+ORPort 31408