console: handle internal.format_yaml exceptions

Currently the call to internal.format_yaml in output_handlers["yaml"]
is covered by pcall only for `status == true`, however the opposite
case also can raise an exception. This patch adds the missed exception
handling. Two distinct calls are required, because it is not possible to
assing variadic arguments (...) to a variable if some of them is nil.
If the first call fails, internal.format_yaml will be called for the
second time. Hopefully, it will not fail during formatting of the error
message received from libyaml.

Before:
```
tarantool> require('net.box').self:call('\x80')
LuajitError: builtin/box/console.lua:710: expected SCALAR, SEQUENCE-START,
    MAPPING-START, or ALIAS fatal error, exiting the event loop
~/test$ echo $?
0
~/test$
```

After:
```
tarantool> require('net.box').self:call('\x80')
---
- error: 'console: an exception occurred when formatting the output:
    expected SCALAR, SEQUENCE-START, MAPPING-START, or ALIAS'
...

tarantool>
```

Part of tarantool#6781
Part of tarantool#6934

NO_DOC=bugfix
NO_TEST=see later commits
NO_CHANGELOG=see later commits

src/box/lua/console.lua

@@ -51,23 +51,24 @@ local output_handlers = { }
 local output_eos = { ["yaml"] = '\n...\n', ["lua"] = ';' }
 
 output_handlers["yaml"] = function(status, opts, ...)
-    local err
+    local err, ok, res
+     -- Using pcall, because serializer can raise an exception
     if status then
-        -- serializer can raise an exception
-        status, err = pcall(internal.format_yaml, ...)
-        if status then
-            return err
-        else
-            err = 'console: an exception occurred when formatting the output: '..
-                tostring(err)
-        end
+        ok, res = pcall(internal.format_yaml, ...)
     else
         err = ...
         if err == nil then
             err = box.NULL
         end
+        ok, res = pcall(internal.format_yaml, { error = err })
+    end
+    if ok then
+        return res
+    else
+        local m = 'console: exception while formatting the output: "%s"'
+        err = m:format(tostring(res))
+        return internal.format_yaml({ error = err })
     end
-    return internal.format_yaml({ error = err })
 end
 
 --