Don't fail silently when an empty csv is imported

ftl/core/importing.ftl

@@ -115,6 +115,7 @@ importing-cards-added =
         [one] { $count } card added.
        *[other] { $count } cards added.
     }
+importing-file-empty = The file you selected is empty.
 
 ## NO NEED TO TRANSLATE. This text is no longer used by Anki, and will be removed in the future.
 

rslib/src/import_export/mod.rs

@@ -137,6 +137,7 @@ pub enum ImportError {
     TooNew,
     MediaImportFailed { info: String },
     NoFieldColumn,
+    EmptyFile,
 }
 
 impl ImportError {
@@ -148,6 +149,7 @@ impl ImportError {
                 tr.importing_failed_to_import_media_file(info)
             }
             ImportError::NoFieldColumn => tr.importing_file_must_contain_field_column(),
+            ImportError::EmptyFile => tr.importing_file_empty(),
         }
         .into()
     }

rslib/src/import_export/text/csv/metadata.rs

@@ -46,7 +46,12 @@ impl Collection {
         is_html: Option<bool>,
     ) -> Result<CsvMetadata> {
         let mut reader = open_file(path)?;
-        self.get_reader_metadata(&mut reader, delimiter, notetype_id, deck_id, is_html)
+        let meta =
+            self.get_reader_metadata(&mut reader, delimiter, notetype_id, deck_id, is_html)?;
+        if meta.preview.is_empty() {
+            return Err(ImportError::EmptyFile.into());
+        }
+        Ok(meta)
     }
 
     fn get_reader_metadata(