[finsh] change return type of finsh_getchar from ch to int

finsh_getchar invokes getchar, who's return type is int, and return value may < 0, which means error occurred or EOF.
finsh should handle that situation properly, and inform user about the error.

components/finsh/shell.c

@@ -134,12 +134,12 @@ void finsh_set_prompt_mode(rt_uint32_t prompt_mode)
     shell->prompt_mode = prompt_mode;
 }
 
-static char finsh_getchar(void)
+static int finsh_getchar(void)
 {
 #ifdef RT_USING_POSIX
     return getchar();
 #else
-    char ch;
+    int ch;
 
     RT_ASSERT(shell != RT_NULL);
     while (rt_device_read(shell->device, -1, &ch, 1) != 1)
@@ -279,7 +279,7 @@ const char *finsh_get_password(void)
 
 static void finsh_wait_auth(void)
 {
-    char ch;
+    int ch;
     rt_bool_t input_finish = RT_FALSE;
     char password[FINSH_PASSWORD_MAX] = { 0 };
     rt_size_t cur_pos = 0;
@@ -295,6 +295,11 @@ static void finsh_wait_auth(void)
             {
                 /* read one character from device */
                 ch = finsh_getchar();
+                if (ch < 0)
+                {
+                    rt_kprintf("finsh getchar error\n");
+                    continue;
+                }
 
                 if (ch >= ' ' && ch <= '~' && cur_pos < FINSH_PASSWORD_MAX)
                 {
@@ -460,7 +465,7 @@ static void shell_push_history(struct finsh_shell *shell)
 
 void finsh_thread_entry(void *parameter)
 {
-    char ch;
+    int ch;
 
     /* normal is echo mode */
 #ifndef FINSH_ECHO_DISABLE_DEFAULT
@@ -503,6 +508,11 @@ void finsh_thread_entry(void *parameter)
     while (1)
     {
         ch = finsh_getchar();
+        if (ch < 0)
+        {
+            rt_kprintf("finsh getchar error\n");
+            continue;
+        }
 
         /*
          * handle control key