Disable input polling when the context menu kludge is active

It can, if the selection is changed in that narrow window, cause
bogus deletion of the selection.

Issue #3273

Author: marijnh

lib/codemirror.js

@@ -1389,9 +1389,11 @@
       // possible when it is clear that nothing happened. hasSelection
       // will be the case when there is a lot of text in the textarea,
       // in which case reading its value would be expensive.
-      if (!cm.state.focused || (hasSelection(input) && !prevInput) ||
+      if (this.contextMenuPending || !cm.state.focused ||
+          (hasSelection(input) && !prevInput) ||
           isReadOnly(cm) || cm.options.disableInput || cm.state.keySeq)
         return false;
+
       // See paste handler for more on the fakedLastChar kludge
       if (cm.state.pasteIncoming && cm.state.fakedLastChar) {
         input.value = input.value.substring(0, input.value.length - 1);