fix #1228 doc.as may not work

Author: sumneko

Diff for: changelog.md

@@ -23,6 +23,7 @@
   local n2 = f(0)    -- `n2` is `number`
   local n3 = f(0, 0) -- `n3` is `string`
   ```
+* `FIX` [#1228](https://github.com/sumneko/lua-language-server/issues/1228)
 
 ## 3.3.1
 `2022-6-17`

Diff for: script/vm/compiler.lua

@@ -629,7 +629,7 @@ local function bindAs(source)
     local root = guide.getRoot(source)
     local docs = root.docs
     if not docs then
-        return
+        return false
     end
     local ases = docs._asCache
     if not ases then
@@ -645,19 +645,20 @@ local function bindAs(source)
         end)
     end
 
+    if #ases == 0 then
+        return false
+    end
+
     local max = #ases
     local index
     local left  = 1
     local right = max
     for _ = 1, 1000 do
-        index = left + (right - left) // 2
-        if index <= left then
+        if left == right then
             index = left
             break
-        elseif index >= right then
-            index = right
-            break
         end
+        index = left + (right - left) // 2
         local doc = ases[index]
         if doc.originalComment.start < source.finish + 2 then
             left = index + 1

Diff for: test/type_inference/init.lua

@@ -2998,3 +2998,9 @@ local t
 
 local <?n?> = t[i]
 ]]
+
+TEST 'string' [=[
+local x = true
+local y = x--[[@as integer]] --is `integer` here
+local z = <?x?>--[[@as string]] --is `true` here
+]=]