Fix dialyzer no_match warning
Fix dialyzer no_match warning

Before this change, the index macro was generating these warnings when
used:

lib/ex_admin/index.ex:149: The variable _@48 can never match since
previous clauses completely covered the type 'nil'
lib/ex_admin/index.ex:149: The variable _@18 can never match since
previous clauses completely covered the type 'nil'

The call to unquote(contents) could change the value of that variable,
but dialyzer isn't smart enough to realize that.

Kociamber/ex_admin,whitepaperclip/ex_admin,smpallen99/ex_admin,kleinernik/ex_admin,Kociamber/ex_admin,whitepaperclip/ex_admin,kleinernik/ex_admin,smpallen99/ex_admin