AsciiDoc multi-page HTML splitter should give nicer message in case page title heading is lacking an id
Revision d68c9772b, build the tooldef docs:
```
java.lang.RuntimeException: Failed to analyze AsciiDoc source file: /newhome/alberth/work/eclipse/oct2024/escet/tooldef/org.eclipse.escet.tooldef.documentation/asciidoc/user-manual/language.asciidoc
at org.eclipse.escet.common.asciidoc.html.multipage.AsciiDocMultiPageHtmlSplitter.splitHtml(AsciiDocMultiPageHtmlSplitter.java:171)
at org.eclipse.escet.common.asciidoc.html.multipage.AsciiDocMultiPageHtmlSplitterMojo.execute(AsciiDocMultiPageHtmlSplitterMojo.java:81)
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:126)
at org.apache.maven.lifecycle.internal.MojoExecutor.doExecute2(MojoExecutor.java:328)
at org.apache.maven.lifecycle.internal.MojoExecutor.doExecute(MojoExecutor.java:316)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:212)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:174)
at org.apache.maven.lifecycle.internal.MojoExecutor.access$000(MojoExecutor.java:75)
at org.apache.maven.lifecycle.internal.MojoExecutor$1.run(MojoExecutor.java:162)
at org.apache.maven.plugin.DefaultMojosExecutionStrategy.execute(DefaultMojosExecutionStrategy.java:39)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:159)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:105)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:73)
at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build(SingleThreadedBuilder.java:53)
at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:118)
at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:261)
at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:173)
at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:101)
at org.apache.maven.cli.MavenCli.execute(MavenCli.java:906)
at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:283)
at org.apache.maven.cli.MavenCli.main(MavenCli.java:206)
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
at java.base/java.lang.reflect.Method.invoke(Method.java:580)
at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:255)
at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:201)
at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:361)
at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:314)
Caused by: com.google.common.base.VerifyException
at com.google.common.base.Verify.verify(Verify.java:102)
at org.eclipse.escet.common.asciidoc.html.multipage.AsciiDocSourceFileAnalyzer.analyze(AsciiDocSourceFileAnalyzer.java:89)
at org.eclipse.escet.common.asciidoc.html.multipage.AsciiDocMultiPageHtmlSplitter.splitHtml(AsciiDocMultiPageHtmlSplitter.java:169)
... 26 more
```
issue