esp32/mphalport: Actually read from dupterm in mp_hal_stdin_rx_chr().

The esp32 port (and esp8266) doesn't read from dupterm in
`mp_hal_stdin_rx_chr()` is because it uses `os.dupterm_notify()` instead,
which forces a read of the dupterm sources from Python.  That function
should be called when it's known that there is input to read.

Nevertheless, this commit adds code to explicitly poll dupterm in
`mp_hal_stdin_rx_chr()`, following other ports like rp2.

Signed-off-by: Matthias Urlichs <matthias@urlichs.de>

Author: smurfix

ports/esp32/mphalport.c

@@ -138,6 +138,12 @@ int mp_hal_stdin_rx_chr(void) {
         if (c != -1) {
             return c;
         }
+        #if MICROPY_PY_OS_DUPTERM
+        int dupterm_c = mp_os_dupterm_rx_chr();
+        if (dupterm_c >= 0) {
+            return dupterm_c;
+        }
+        #endif
         MICROPY_EVENT_POLL_HOOK
     }
 }