[archive,sqlite-] guess sqlite/tar/zip filetypes confidently

And never guess that empty files are tarfiles.

visidata/loaders/archive.py

@@ -5,18 +5,21 @@
 from visidata.loaders import unzip_http
 
 from visidata import vd, VisiData, asyncthread, Sheet, Progress, Menu, options
-from visidata import ColumnAttr, Column, Path
+from visidata import ColumnAttr, Column, Path, filesize
 from visidata.type_date import date
 
 @VisiData.api
 def guess_zip(vd, p):
     if not p.is_url() and zipfile.is_zipfile(p.open_bytes()):
-        return dict(filetype='zip')
+        return dict(filetype='zip', _likelihood=10)
 
 @VisiData.api
 def guess_tar(vd, p):
+    # an empty file will pass is_tarfile(), but can't be opened by tarfile.open()
+    if filesize(p) == 0:
+        return None
     if tarfile.is_tarfile(p.open_bytes()):
-        return dict(filetype='tar')
+        return dict(filetype='tar', _likelihood=10)
 
 @VisiData.api
 def open_zip(vd, p):

visidata/loaders/sqlite.py

@@ -20,7 +20,7 @@ def requery(url, **kwargs):
 @VisiData.api
 def guess_sqlite(vd, p):
     if p.open_bytes().read(16).startswith(b'SQLite format'):
-        return dict(filetype='sqlite')
+        return dict(filetype='sqlite', _likelihood=10)
 
 
 @VisiData.api