Check the address on the BTags paths too

The sink and the CTRL-O Show callback passed the raw field into the Ex command.
A custom tag command can emit any address, so put it through the same check as
:Tags. The BTags source aligns its columns, hence the strip.

autoload/fzf/vim.vim

@@ -549,9 +549,11 @@ endfunction
 let s:tag_address_part = '\%(\d\+\|/\%(\\.\|[^/\\]\)*/\|?\%(\\.\|[^?\\]\)*?\)'
 let s:tag_address_open = '\%(/\%(\\.\|[^/\\]\)*\|?\%(\\.\|[^?\\]\)*\)'
 function! s:tag_address(rest)
-  let address = matchstr(a:rest,
+  " :BTags aligns its columns, so its field arrives padded
+  let rest = s:strip(a:rest)
+  let address = matchstr(rest,
         \ '^'.s:tag_address_part.'\%(;'.s:tag_address_part.'\)*\ze\%(;"\|$\)')
-  return empty(address) ? matchstr(a:rest, '^'.s:tag_address_open.'$') : address
+  return empty(address) ? matchstr(rest, '^'.s:tag_address_open.'$') : address
 endfunction
 
 " [key, [filename, [stay_on_edit: 0]]]
@@ -764,8 +766,12 @@ function! s:goto_entry(winid, bufnr, dir, kind, entry) abort
     if len(parts) < 3 || !bufexists(a:bufnr)
       return
     endif
+    let excmd = s:tag_address(parts[2])
+    if empty(excmd)
+      return
+    endif
     let cmds = ['keepalt keepjumps hide buffer '.a:bufnr,
-          \ 'sandbox keepjumps '.parts[2], 'normal! zvzz']
+          \ 'sandbox keepjumps '.excmd, 'normal! zvzz']
   elseif a:kind ==# 'marks'
     " A lowercase mark is local to the buffer the run started on
     let mark = matchstr(entry, '^\s*\zs\S')
@@ -1674,7 +1680,11 @@ function! s:btags_sink(from, lines)
   let qfl = []
   for line in a:lines[1:]
     let parts = split(line, "\t")
-    call s:execute_tag_address(parts[2])
+    let excmd = s:tag_address(parts[2])
+    if empty(excmd)
+      continue
+    endif
+    call s:execute_tag_address(excmd)
     call add(qfl, {'filename': expand('%'), 'lnum': line('.'), 'text': getline('.')})
     if empty(tagname)
       let tagname = s:strip(parts[0])