lib: defer pausing stdin to the next tick

This is done to match the stream implementation, which also
only actually stops reading in the next tick after the `'pause'`
event is emitted.

PR-URL: #19377
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/internal/process/stdio.js

@@ -109,15 +109,22 @@ function setupStdio() {
       stdin._handle.readStop();
     }
 
-    // if the user calls stdin.pause(), then we need to stop reading
-    // immediately, so that the process can close down.
+    // If the user calls stdin.pause(), then we need to stop reading
+    // once the stream implementation does so (one nextTick later),
+    // so that the process can close down.
     stdin.on('pause', () => {
+      process.nextTick(onpause);
+    });
+
+    function onpause() {
       if (!stdin._handle)
         return;
-      stdin._readableState.reading = false;
-      stdin._handle.reading = false;
-      stdin._handle.readStop();
-    });
+      if (stdin._handle.reading && !stdin._readableState.flowing) {
+        stdin._readableState.reading = false;
+        stdin._handle.reading = false;
+        stdin._handle.readStop();
+      }
+    }
 
     return stdin;
   }