plugin: handle sandbox mode gracefully

When the sandbox is active (e.g. while debugging something), certains
commands and expressions are not allowed (see :h sandbox) and may cause
nasty exceptions to be thrown.

So try to catch E48 and handle it gracefully

autoload/airline.vim

@@ -156,7 +156,12 @@ function! airline#update_statusline()
   " Now create the active statusline
   let w:airline_active = 1
   let context = { 'winnr': winnr(), 'active': 1, 'bufnr': winbufnr(winnr()) }
-  call s:invoke_funcrefs(context, g:airline_statusline_funcrefs)
+  try
+    call s:invoke_funcrefs(context, g:airline_statusline_funcrefs)
+  catch /^Vim\%((\a\+)\)\=:E48:/
+    " Catch: Sandbox mode
+    " no-op
+  endtry
 endfunction
 
 " Function to be called to make all statuslines inactive
@@ -186,7 +191,12 @@ function! airline#update_statusline_inactive(range)
             \ 'left_sep': g:airline_left_alt_sep,
             \ 'right_sep': g:airline_right_alt_sep }, 'keep')
     endif
-    call s:invoke_funcrefs(context, g:airline_inactive_funcrefs)
+    try
+      call s:invoke_funcrefs(context, g:airline_inactive_funcrefs)
+    catch /^Vim\%((\a\+)\)\=:E48:/
+      " Catch: Sandbox mode
+      " no-op
+    endtry
   endfor
 endfunction
 

autoload/airline/util.vim

@@ -180,7 +180,12 @@ function! airline#util#doautocmd(event)
     " airline disabled
     return
   endif
-  exe printf("silent doautocmd %s User %s", s:nomodeline, a:event)
+  try
+    exe printf("silent doautocmd %s User %s", s:nomodeline, a:event)
+  catch /^Vim\%((\a\+)\)\=:E48:/
+    " Catch: Sandbox mode
+    " no-op
+  endtry
 endfunction
 
 function! airline#util#themes(match)