git-rm: honor -n flag.

Even when invoked with -n flag, git-rm removed the matching
paths anyway.  Also includes the missing check spotted by
SungHyun Nam, which caused it to segfault.  Now we refuse to run
without any paths.

Signed-off-by: Junio C Hamano <junkio@cox.net>

builtin-rm.c

@@ -83,15 +83,15 @@ int cmd_rm(int argc, const char **argv, char **envp)
 		}
 		die(builtin_rm_usage);
 	}
-	pathspec = get_pathspec(prefix, argv + i);
+	if (argc <= i)
+		usage(builtin_rm_usage);
 
+	pathspec = get_pathspec(prefix, argv + i);
 	seen = NULL;
-	if (pathspec) {
-		for (i = 0; pathspec[i] ; i++)
-			/* nothing */;
-		seen = xmalloc(i);
-		memset(seen, 0, i);
-	}
+	for (i = 0; pathspec[i] ; i++)
+		/* nothing */;
+	seen = xmalloc(i);
+	memset(seen, 0, i);
 
 	for (i = 0; i < active_nr; i++) {
 		struct cache_entry *ce = active_cache[i];
@@ -121,6 +121,9 @@ int cmd_rm(int argc, const char **argv, char **envp)
 		cache_tree_invalidate_path(active_cache_tree, path);
 	}
 
+	if (show_only)
+		return 0;
+
 	/*
 	 * Then, if we used "-f", remove the filenames from the
 	 * workspace. If we fail to remove the first one, we