http2: small fixes to http2 core

A few small changes:
- fix debug statement location
- simplify conditional with returns
- consistent use of template strings

PR-URL: #16327
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

lib/internal/http2/core.js

@@ -881,14 +881,14 @@ class Http2Session extends EventEmitter {
 
     // A stream cannot be made to depend on itself
     if (options.parent === id) {
-      debug(`[${sessionName(this[kType])}] session still connecting. queue ` +
-            'priority');
       throw new errors.TypeError('ERR_INVALID_OPT_VALUE',
                                  'parent',
                                  options.parent);
     }
 
     if (id === undefined) {
+      debug(`[${sessionName(this[kType])}] session still connecting. queue ` +
+            'priority');
       stream.once('ready', submitPriority.bind(this, stream, options));
       return;
     }
@@ -1203,7 +1203,7 @@ function streamOnResume() {
   if (session && !state.reading) {
     state.reading = true;
     assert(session[kHandle].streamReadStart(this[kID]) === undefined,
-           'HTTP/2 Stream #{this[kID]} does not exist. Please report this as ' +
+           `HTTP/2 Stream ${this[kID]} does not exist. Please report this as ` +
            'a bug in Node.js');
   }
 }
@@ -1411,7 +1411,7 @@ class Http2Stream extends Duplex {
       return;
     state.reading = true;
     assert(this[kSession][kHandle].streamReadStart(this[kID]) === undefined,
-           'HTTP/2 Stream #{this[kID]} does not exist. Please report this as ' +
+           `HTTP/2 Stream ${this[kID]} does not exist. Please report this as ` +
            'a bug in Node.js');
   }
 
@@ -2264,16 +2264,14 @@ function connectionListener(socket) {
   const options = this[kOptions] || {};
 
   if (socket.alpnProtocol === false || socket.alpnProtocol === 'http/1.1') {
-    if (options.allowHTTP1 === true) {
-      // Fallback to HTTP/1.1
+    // Fallback to HTTP/1.1
+    if (options.allowHTTP1 === true)
       return httpConnectionListener.call(this, socket);
-    } else if (this.emit('unknownProtocol', socket)) {
-      // Let event handler deal with the socket
+    // Let event handler deal with the socket
+    if (this.emit('unknownProtocol', socket))
       return;
-    } else {
-      // Reject non-HTTP/2 client
-      return socket.destroy();
-    }
+    // Reject non-HTTP/2 client
+    return socket.destroy();
   }
 
   socket.on('error', socketOnError);