Drop a tag address part cut short by a tab

:BTags reads the address field on its own, so ctags writing a tab inside a
pattern leaves it unterminated: '--excmd=combine' gives '5;/^int', whose
fragment matched line 7 instead of 5, silently and with a quickfix item to
match. Keep the parts that did parse, so the line number still stands.

An unterminated pattern is still taken on its own, being the whole address in a
helptags file.

autoload/fzf/vim.vim

@@ -550,19 +550,26 @@ endfunction
 " Address of a tag, given the rest of the line after the file name. Only the
 " forms a tags file is meant to hold, a line number and a search pattern,
 " chained with ';' for '--excmd=combine' and cut at the ';"' terminator as
-" Vim's find_extra() does. The last pattern can be left unterminated, as a
+" Vim's find_extra() does. Returns an empty string for anything else, which is
-" field holding a tab arrives cut short; it then runs to the end of the line,
+" then not run.
-" taking any '|' or ';' with it, so it cannot chain a command. Returns an
+"
-" empty string for anything else, which is then not run.
+" A pattern holding a tab reaches :BTags cut short, since it reads the field on
+" its own. Such a fragment matches the wrong line, so keep only the parts before
+" it, and accept an unterminated pattern alone, which is the whole address in a
+" helptags file. Running to the end of the line, it takes any '|' or ';' with it,
+" so it cannot chain a command either.
 let s:tag_address_part = '\%(\d\+\|/\%(\\.\|[^/\\]\)*/\|?\%(\\.\|[^?\\]\)*?\)'
 let s:tag_address_open = '\%(/\%(\\.\|[^/\\]\)*\|?\%(\\.\|[^?\\]\)*\)'
 function! s:tag_address(rest)
   " :BTags aligns its columns, so its field arrives padded
   let rest = s:strip(a:rest)
-  let address = matchstr(rest,
+  let chain = '^'.s:tag_address_part.'\%(;'.s:tag_address_part.'\)*'
-        \ '^'.s:tag_address_part.'\%(;'.s:tag_address_part.'\)*\ze\%(;"\|$\)')
+  let address = matchstr(rest, chain.'\ze\%(;"\|$\)')
-  return empty(address) ? matchstr(rest,
+  if !empty(address)
-        \ '^\%('.s:tag_address_part.';\)*'.s:tag_address_open.'$') : address
+    return address
+  endif
+  let address = matchstr(rest, chain.'\ze;[/?]')
+  return empty(address) ? matchstr(rest, '^'.s:tag_address_open.'$') : address
 endfunction
 
 " [key, [filename, [stay_on_edit: 0]]]