empty input stream

#146
use `noInput` class
also fixing escKey to exit sleep mode consuming input on first check.

Author: neu-rah

src/io.h

@@ -20,6 +20,14 @@
         inline void fieldOff() {setFieldMode(false);}
     };
 
+    class noInput:public menuIn {
+    public:
+      size_t write(uint8_t) override {}
+      int available() override {return 0;}
+      int read() override {return -1;}
+      int peek() override {return -1;}
+    };
+
     #ifdef MENU_ASYNC
       class StringStream:public menuIn {
         public:

src/nav.cpp

@@ -111,7 +111,8 @@ result navNode::sysEvent(eventMask e,idx_t i) {
 void navRoot::doInput(menuIn& in) {
   trace(Serial<<"navRoot::doInput"<<endl);
   if (sleepTask) {
-    if (options->getCmdChar(enterCmd)==in.read() || options->getCmdChar(escCmd)==in.read()) idleOff();
+    char c=in.read();
+    if (options->getCmdChar(enterCmd)==c || options->getCmdChar(escCmd)==c) idleOff();
   } else {
     idx_t inputBurstCnt=inputBurst+1;
     //if (in.available())