cli: handle getch error

Handle getch error (when getch return 0x0) to avoid display issue
in the console.

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>

common/cli_readline.c

@@ -273,6 +273,10 @@ static int cread_line(const char *const prompt, char *buf, unsigned int *len,
 
 		ichar = getcmd_getch();
 
+		/* ichar=0x0 when error occurs in U-Boot getc */
+		if (!ichar)
+			continue;
+
 		if ((ichar == '\n') || (ichar == '\r')) {
 			putc('\n');
 			break;