input_file, input_curl: check URL type before attempting to open

Don't attempt to open a HTTP URL as a local file, and don't send a
local path to libcurl.

src/input_curl.c

@@ -473,6 +473,9 @@ input_curl_open(struct input_stream *is, const char *url)
 	struct input_curl *c;
 	bool ret;
 
+	if (strncmp(url, "http://", 7) != 0)
+		return false;
+
 	c = g_new0(struct input_curl, 1);
 	c->url = g_strdup(url);
 	INIT_LIST_HEAD(&c->buffers);

src/input_file.c

@@ -26,6 +26,9 @@ input_file_open(struct input_stream *is, const char *filename)
 {
 	FILE *fp;
 
+	if (filename[0] != '/')
+		return false;
+
 	fp = fopen(filename, "r");
 	if (!fp) {
 		is->error = errno;