Report an error when the document template max bytes is zero

crates/milli/src/error.rs

@@ -386,6 +386,8 @@ and can not be more than 511 bytes.", .document_id.to_string()
     DocumentEditionRuntimeError(Box<EvalAltResult>),
     #[error("Document edition runtime error encountered while compiling the function: {0}")]
     DocumentEditionCompilationError(rhai::ParseError),
+    #[error("`.chat.documentTemplateMaxBytes`: `documentTemplateMaxBytes` cannot be zero")]
+    InvalidChatSettingsDocumentTemplateMaxBytes,
     #[error("{0}")]
     DocumentEmbeddingError(String),
 }