patch 9.1.1661: Coverity finds a few issues in clientserver.c

Problem:  Coverity finds a few issues in clientserver.c
          (also by Tony Mechelynck)
Solution: Fix issues and warnings (Foxe Chen)

closes: #18057

Signed-off-by: Foxe Chen <chen.foxe@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/testdir/test_remote.vim

@@ -15,6 +15,19 @@ func Verify_remote_feature_works()
   enew
   let buf = RunVimInTerminal('--servername XVIMTEST', {'rows': 8})
   call TermWait(buf)
+
+  " For some reason when the socket server is being used, the terminal Vim never
+  " receives the `:w! XVimRemoteTest.txt` command from term_sendkeys.
+  if has('socketserver') && !has('X11')
+    if match(serverlist(), "XVIMTEST") == -1
+      call StopVimInTerminal(buf)
+      throw s:skip
+    endif
+
+    let s:remote = 1
+    return
+  endif
+
   let cmd = GetVimCommandCleanTerm() .. '--serverlist'
   call term_sendkeys(buf, ":r! " .. cmd .. "\<CR>")
   call TermWait(buf)