Fix #1816 - Fix a type error in the initialize message handler

autoload/ale/lsp.vim

@@ -256,7 +256,8 @@ function! ale#lsp#HandleOtherInitializeResponses(conn, response) abort
     endif
 
     if get(a:response, 'method', '') is# ''
-        if has_key(get(a:response, 'result', {}), 'capabilities')
+        if type(get(a:response, 'result')) is v:t_dict
+        \&& has_key(a:response.result, 'capabilities')
             call s:UpdateCapabilities(a:conn, a:response.result.capabilities)
 
             for [l:dir, l:project] in l:uninitialized_projects

test/lsp/test_other_initialize_message_handling.vader

@@ -181,3 +181,10 @@ Execute(Disabled capabilities should be recognised correctly):
   \   },
   \ },
   \ b:conn
+
+Execute(Results that are not dictionaries should be handled correctly):
+  call ale#lsp#HandleOtherInitializeResponses(b:conn, {
+  \ 'jsonrpc': '2.0',
+  \ 'id': 1,
+  \ 'result': v:null,
+  \})