avformat/hlsenc: fix cid 1401346 Dereferencing pointer error

check if proto is null before av_strcasecmp
CID:  1401346
Signed-off-by: Steven Liu <lq@chinaffmpeg.org>

libavformat/hlsenc.c

@@ -668,11 +668,11 @@ static void hls_free_segments(HLSSegment *p)
 static void set_http_options(AVFormatContext *s, AVDictionary **options, HLSContext *c)
 {
     const char *proto = avio_find_protocol_name(s->filename);
-    int http_base_proto = !av_strcasecmp(proto, "http") || !av_strcasecmp(proto, "https");
+    int http_base_proto = proto ? (!av_strcasecmp(proto, "http") || !av_strcasecmp(proto, "https")) : 0;
 
     if (c->method) {
         av_dict_set(options, "method", c->method, 0);
-    } else if (proto && http_base_proto) {
+    } else if (http_base_proto) {
         av_log(c, AV_LOG_WARNING, "No HTTP method set, hls muxer defaulting to method PUT.\n");
         av_dict_set(options, "method", "PUT", 0);
     }