Revert "bugfix: ngx.base: decode_base64url/encode_base64url: worked around a bug in LuaJIT's allocation sinking optimizer which might lead to NULL cdata pointers and segfaults."

This reverts commit c99fbaf following
the LuaJIT at openresty/luajit2#46.

Author: thibaultcha

lib/ngx/base64.lua

@@ -46,16 +46,18 @@ function _M.encode_base64url(s)
 
     local len = #s
     local trans_len = base64_encoded_length(len)
+    local src = src_str_t[0]
+    local dst = dst_str_t[0]
 
-    src_str_t[0].data = s
-    src_str_t[0].len = len
+    src.data = s
+    src.len = len
 
-    dst_str_t[0].data = get_string_buf(trans_len)
-    dst_str_t[0].len = trans_len
+    dst.data = get_string_buf(trans_len)
+    dst.len = trans_len
 
     C.ngx_encode_base64url(dst_str_t, src_str_t)
 
-    return ffi_str(dst_str_t[0].data, dst_str_t[0].len)
+    return ffi_str(dst.data, dst.len)
 end
 
 
@@ -66,19 +68,21 @@ function _M.decode_base64url(s)
 
     local len = #s
     local trans_len = base64_decoded_length(len)
+    local src = src_str_t[0]
+    local dst = dst_str_t[0]
 
-    src_str_t[0].data = s
-    src_str_t[0].len = len
+    src.data = s
+    src.len = len
 
-    dst_str_t[0].data = get_string_buf(trans_len)
-    dst_str_t[0].len = trans_len
+    dst.data = get_string_buf(trans_len)
+    dst.len = trans_len
 
     local ret = C.ngx_decode_base64url(dst_str_t, src_str_t)
     if ret == NGX_ERROR then
         return nil, "invalid input"
     end
 
-    return ffi_str(dst_str_t[0].data, dst_str_t[0].len)
+    return ffi_str(dst.data, dst.len)
 end