searchcount: Ignore errors from searchcount() function

If the search regex causes an error, an ugly error message is thrown,
so ignore errors in that case silently.

closes #2216

autoload/airline/extensions/searchcount.vim

@@ -18,6 +18,7 @@ function! airline#extensions#searchcount#apply(...) abort
 endfunction
 
 function! airline#extensions#searchcount#status() abort
+  try
     let result = searchcount(#{recompute: 1, maxcount: -1})
     if empty(result) || result.total ==# 0
       return ''
@@ -36,4 +37,7 @@ function! airline#extensions#searchcount#status() abort
     endif
     return printf('%s[%d/%d]', @/,
           \		result.current, result.total)
+  catch
+    return ''
+  endtry
 endfunction