repl: check for precise values rather than falsy in loops

This prepares the code for the no-cond-assign ESLint rule.

PR-URL: #41614
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

lib/repl.js

@@ -381,7 +381,7 @@ function REPLServer(prompt,
     paused = false;
     let entry;
     const tmpCompletionEnabled = self.isCompletionEnabled;
-    while (entry = ArrayPrototypeShift(pausedBuffer)) {
+    while ((entry = ArrayPrototypeShift(pausedBuffer)) !== undefined) {
       const { 0: type, 1: payload, 2: isCompletionEnabled } = entry;
       switch (type) {
         case 'key': {
@@ -1450,7 +1450,7 @@ function complete(line, callback) {
       ArrayPrototypePush(completionGroups,
                          getGlobalLexicalScopeNames(this[kContextId]));
       let contextProto = this.context;
-      while (contextProto = ObjectGetPrototypeOf(contextProto)) {
+      while ((contextProto = ObjectGetPrototypeOf(contextProto)) !== null) {
         ArrayPrototypePush(completionGroups,
                            filteredOwnPropertyNames(contextProto));
       }