nginx rewrite fixes

nginx.conf checks for …/_index$w3tc_rewrite.html$w3tc_enc files but the $w3tc_rewrite is 1 or 0

before:

if ($http_cookie ~* "(w3tc_preview)") {
    set $w3tc_rewrite _preview;
}
...
if (!-f "$document_root/wp-content/cache/page_enhanced/$http_host/$request_uri/_index$w3tc_rewrite.html$w3tc_enc") {
  set $w3tc_rewrite 0;
}
if ($w3tc_rewrite = 1) {
    rewrite .* "/wp-content/cache/page_enhanced/$http_host/$request_uri/_index$w3tc_rewrite.html$w3tc_enc" last;
}

fix:

set $w3tc_preview "";
if ($http_cookie ~* "(w3tc_preview)") {
    set $w3tc_preview _preview;
}
...
if (!-f "$document_root/wp-content/cache/page_enhanced/$http_host/$request_uri/_index$w3tc_preview.html$w3tc_enc") {
  set $w3tc_rewrite 0;
}
if ($w3tc_rewrite = 1) {
    rewrite .* "/wp-content/cache/page_enhanced/$http_host/$request_uri/_index$w3tc_preview.html$w3tc_enc" last;
}

https://wordpress.org/plugins/w3-total-cache/