BUG: Fix line offset for full module Browse git link

Fixes: #296
Co-authored-by: fweisser <59307989+fweisser@users.noreply.github.com>

Author: kernc

pdoc/html_helpers.py

@@ -566,6 +566,7 @@ def format_git_link(template: str, dobj: pdoc.Doc):
             path = path.replace('\\', '/')
 
         lines, start_line = inspect.getsourcelines(dobj.obj)
+        start_line = start_line or 1  # GH-296
         end_line = start_line + len(lines) - 1
         url = template.format(**locals())
         return url