No longer says "unknown command" to an empty input string in the debugger.

This fixes bug #189.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@16452 a95241bf-73f2-0310-859d-f6bbb57e9c96

src/system/kernel/debug/debug.c

@@ -253,7 +253,7 @@ parse_line(char *buf, char **argv, int *argc, int max_args)
 
 	strcpy(sParseLine, buf);
 
-	if (!isspace(sParseLine[0])) {
+	if (sParseLine[0] != '\0' && !isspace(sParseLine[0])) {
 		argv[0] = sParseLine;
 		*argc = 1;
 	} else