Various minor fixes following a pass of cppcheck static analyzer

imgui_demo.cpp

@@ -1871,6 +1871,7 @@ struct ExampleAppConsole
     ExampleAppConsole()
     {
         ClearLog();
+        memset(InputBuf, 0, sizeof(InputBuf));
         HistoryPos = -1;
         Commands.push_back("HELP");
         Commands.push_back("HISTORY");