perf(diagnostic): avoid first send

If the cache is equal to the full result, we should avoid to notify
client during first stage.

Author: kevinhwang91

script/provider/diagnostic.lua

@@ -256,13 +256,13 @@ function m.doDiagnostic(uri, isScopeDiag)
         end
     end
 
+    pushResult()
+
     -- always re-sent diagnostics of current file
     if not isScopeDiag then
         m.cache[uri] = nil
     end
 
-    pushResult()
-
     local lastPushClock = time.time()
     ---@async
     xpcall(core, log.error, uri, isScopeDiag, function (result)