FIX: watchdog timeout, while waiting for input

* add WATCHDOG_RESET to !tstc() loops
* prevents watchdog timeout, while waiting for input,
  if CONFIG_BOOT_RETRY_TIME or CONFIG_SHOW_ACTIVITY defined

Signed-off-by: Jens Scharsig <js_at_ng@scharsoft.de>
diff --git a/common/main.c b/common/main.c
index 3949a5b..f7e7c1c 100644
--- a/common/main.c
+++ b/common/main.c
@@ -730,6 +730,7 @@
 		while (!tstc()) {	/* while no incoming data */
 			if (retry_time >= 0 && get_ticks() > endtime)
 				return (-2);	/* timed out */
+			WATCHDOG_RESET();
 		}
 #endif
 
@@ -997,6 +998,7 @@
 		while (!tstc()) {	/* while no incoming data */
 			if (retry_time >= 0 && get_ticks() > endtime)
 				return (-2);	/* timed out */
+			WATCHDOG_RESET();
 		}
 #endif
 		WATCHDOG_RESET();		/* Trigger watchdog, if needed */
@@ -1005,6 +1007,7 @@
 		while (!tstc()) {
 			extern void show_activity(int arg);
 			show_activity(0);
+			WATCHDOG_RESET();
 		}
 #endif
 		c = getc();