Joex error if an email with empty body is used

You get the following log.

```
docspell-joex1 | 2025.02.10 10:01:54:0001 [io-comp...] [ERROR] docspell.scheduler.impl.SchedulerImpl.wrapTask:304 - Job Ey7pNotye.../1/process-item/High execution failed. Retrying later.
docspell-joex1 | com.sun.mail.util.DecodingException: BASE64Decoder: Error in encoded stream: needed 4 valid base64 characters but only got 1 before EOF, the 10 most recent characters were: "BkjFn06VTj"
docspell-joex1 | at com.sun.mail.util.BASE64DecoderStream.decode(BASE64DecoderStream.java:243)
docspell-joex1 | at com.sun.mail.util.BASE64DecoderStream.read(BASE64DecoderStream.java:124)
docspell-joex1 | at java.io.FilterInputStream.read(FilterInputStream.java:95)
docspell-joex1 | at emil.javamail.conv.BodyDecode$.streamToByteVector(BodyDecode.scala:244)
docspell-joex1 | at emil.javamail.conv.BodyDecode$.emil$javamail$conv$BodyDecode$$loadPart(BodyDecode.scala:250)
docspell-joex1 | at emil.javamail.conv.BodyDecode.$anonfun$attachmentDecode$1(BodyDecode.scala:38)
docspell-joex1 | at emil.javamail.conv.Conv$.emil$javamail$conv$Conv$$$anonfun$apply$1(Conv.scala:18)
docspell-joex1 | at emil.javamail.conv.Conv$$anonfun$apply$2.convert(Conv.scala:18)
docspell-joex1 | at emil.javamail.conv.BodyDecode.decodePart(BodyDecode.scala:110)
docspell-joex1 | at emil.javamail.conv.BodyDecode.$anonfun$decodePart$2(BodyDecode.scala:104)
docspell-joex1 | at scala.collection.IterableOnceOps.foldLeft(IterableOnce.scala:687)
docspell-joex1 | at scala.collection.IterableOnceOps.foldLeft$(IterableOnce.scala:721)
docspell-joex1 | at scala.collection.AbstractIterable.foldLeft(Iterable.scala:935)
docspell-joex1 | at emil.javamail.conv.BodyDecode.decodePart(BodyDecode.scala:81)
docspell-joex1 | at emil.javamail.conv.BodyDecode.$anonfun$mailBodyDecode$2(BodyDecode.scala:58)
docspell-joex1 | at emil.javamail.internal.Util$.$anonfun$withReadFolder$3(Util.scala:26)
docspell-joex1 | at scala.Option.getOrElse(Option.scala:201)
docspell-joex1 | at emil.javamail.internal.Util$.withReadFolder(Util.scala:26)
docspell-joex1 | at emil.javamail.conv.BodyDecode.$anonfun$mailBodyDecode$1(BodyDecode.scala:58)
docspell-joex1 | at emil.javamail.conv.Conv$.emil$javamail$conv$Conv$$$anonfun$apply$1(Conv.scala:18)
docspell-joex1 | at emil.javamail.conv.Conv$$anonfun$apply$2.convert(Conv.scala:18)
docspell-joex1 | at emil.javamail.conv.BodyDecode.$anonfun$mailDecode$3(BodyDecode.scala:130)
docspell-joex1 | at emil.javamail.internal.Util$.$anonfun$withReadFolder$3(Util.scala:26)
docspell-joex1 | at scala.Option.getOrElse(Option.scala:201)
docspell-joex1 | at emil.javamail.internal.Util$.withReadFolder(Util.scala:26)
docspell-joex1 | at emil.javamail.conv.BodyDecode.$anonfun$mailDecode$2(BodyDecode.scala:118)
docspell-joex1 | at emil.javamail.internal.ThreadClassLoader$.apply(ThreadClassLoader.scala:10)
docspell-joex1 | at emil.javamail.conv.BodyDecode.$anonfun$mailDecode$1(BodyDecode.scala:118)
docspell-joex1 | at emil.javamail.conv.Conv$.emil$javamail$conv$Conv$$$anonfun$apply$1(Conv.scala:18)
docspell-joex1 | at emil.javamail.conv.Conv$$anonfun$apply$2.convert(Conv.scala:18)
docspell-joex1 | at emil.javamail.JavaMailEmil$.$anonfun$mailFromByteArray$2(JavaMailEmil.scala:94)
docspell-joex1 | at emil.javamail.internal.ThreadClassLoader$.apply(ThreadClassLoader.scala:10)
docspell-joex1 | at emil.javamail.JavaMailEmil$.$anonfun$mailFromByteArray$1(JavaMailEmil.scala:87)
docspell-joex1 | at delay @ emil.javamail.JavaMailEmil$.mailFromByteArray(JavaMailEmil.scala:87)
docspell-joex1 | at flatMap @ fs2.Compiler$Target.flatMap(Compiler.scala:163)
docspell-joex1 | at handleErrorWith @ fs2.Compiler$Target.handleErrorWith(Compiler.scala:161)
docspell-joex1 | at flatMap @ fs2.Compiler$Target.flatMap(Compiler.scala:163)
docspell-joex1 | at get @ fs2.internal.Scope.openScope(Scope.scala:275)
docspell-joex1 | at flatMap @ fs2.Compiler$Target.flatMap(Compiler.scala:163)
docspell-joex1 | at flatMap @ fs2.Compiler$Target.flatMap(Compiler.scala:163)
docspell-joex1 | at flatMap @ fs2.Compiler$Target.flatMap(Compiler.scala:163)
docspell-joex1 | at flatMap @ fs2.Pull$.goEval$1(Pull.scala:1090)
docspell-joex1 | at get @ fs2.internal.Scope.openScope(Scope.scala:275)
docspell-joex1 | at flatMap @ fs2.Compiler$Target.flatMap(Compiler.scala:163)
docspell-joex1 | at flatMap @ fs2.Compiler$Target.flatMap(Compiler.scala:163)
docspell-joex1 | at flatMap @ fs2.Pull$.fs2$Pull$$interruptGuard$1(Pull.scala:952)
docspell-joex1 | at get @ fs2.internal.Scope.openScope(Scope.scala:275)
docspell-joex1 | at flatMap @ fs2.Compiler$Target.flatMap(Compiler.scala:163)
docspell-joex1 | at flatMap @ fs2.Compiler$Target.flatMap(Compiler.scala:163)
docspell-joex1 |
docspell-joex1 | 2025.02.10 10:01:54:0000 [io-comp...] [ERROR] docspell.scheduler.impl.LogSink.logInternal:49 - >>> 2025-02-10T09:01:54.899212307Z Error Ey7pNotye.../1/process-item/High: Job Ey7pNotye.../1/process-item/High execution failed. Retrying later.
```

Even if an email is empty. I do want the HTML to be generated, because my application expects each email to have a HTML even though that might be empty.