avformat/hlsenc: fix segfault when using -hls_segment_type fmp4 with -hls_segment_filename

previously, specifying -hls_segment_filename meant
s->base_output_dirname was never set, causing a segfault:

(lldb) bt
* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x0)
* frame #0: 0x00007fffbf7d82d0 libsystem_platform.dylib`_platform_strcmp + 80
frame #1: 0x00000001005f4dcf libavformat.57.dylib`io_open_default(s=0x000000010481cc00, pb=0x0000000104806020, url=0x0000000000000000, flags=2, options=0x0000000000000000) at options.c:107
frame #2: 0x0000000100528968 libavformat.57.dylib`hls_mux_init(s=0x000000010481cc00) at hlsenc.c:595
frame #3: 0x00000001005273cb libavformat.57.dylib`hls_write_header(s=0x000000010481cc00) at hlsenc.c:1518
frame #4: 0x00000001005c08d0 libavformat.57.dylib`write_header_internal(s=0x000000010481cc00) at mux.c:486
frame #5: 0x00000001005c0774 libavformat.57.dylib`avformat_write_header(s=0x000000010481cc00, options=0x00000001029026e8) at mux.c:539

libavformat/hlsenc.c

@@ -1441,32 +1441,33 @@ static int hls_write_header(AVFormatContext *s)
         } else {
             av_strlcat(hls->basename, pattern, basename_size);
         }
+    }
 
-        if (av_strcasecmp(hls->fmp4_init_filename, "init.mp4")) {
-            int fmp4_init_filename_len = strlen(hls->fmp4_init_filename) + 1;
-            hls->base_output_dirname = av_malloc(fmp4_init_filename_len);
-            if (!hls->base_output_dirname) {
-                ret = AVERROR(ENOMEM);
-                goto fail;
-            }
-            av_strlcpy(hls->base_output_dirname, hls->fmp4_init_filename, fmp4_init_filename_len);
-        } else {
-            hls->base_output_dirname = av_malloc(basename_size);
-            if (!hls->base_output_dirname) {
-                ret = AVERROR(ENOMEM);
-                goto fail;
-            }
+    if (av_strcasecmp(hls->fmp4_init_filename, "init.mp4")) {
+        int fmp4_init_filename_len = strlen(hls->fmp4_init_filename) + 1;
+        hls->base_output_dirname = av_malloc(fmp4_init_filename_len);
+        if (!hls->base_output_dirname) {
+            ret = AVERROR(ENOMEM);
+            goto fail;
+        }
+        av_strlcpy(hls->base_output_dirname, hls->fmp4_init_filename, fmp4_init_filename_len);
+    } else {
+        hls->base_output_dirname = av_malloc(basename_size);
+        if (!hls->base_output_dirname) {
+            ret = AVERROR(ENOMEM);
+            goto fail;
+        }
 
-            av_strlcpy(hls->base_output_dirname, s->filename, basename_size);
-            p = strrchr(hls->base_output_dirname, '/');
-            if (p) {
-                *(p + 1) = '\0';
-                av_strlcat(hls->base_output_dirname, hls->fmp4_init_filename, basename_size);
-            } else {
-                av_strlcpy(hls->base_output_dirname, hls->fmp4_init_filename, basename_size);
-            }
+        av_strlcpy(hls->base_output_dirname, s->filename, basename_size);
+        p = strrchr(hls->base_output_dirname, '/');
+        if (p) {
+            *(p + 1) = '\0';
+            av_strlcat(hls->base_output_dirname, hls->fmp4_init_filename, basename_size);
+        } else {
+            av_strlcpy(hls->base_output_dirname, hls->fmp4_init_filename, basename_size);
         }
     }
+
     if (!hls->use_localtime) {
         ret = sls_flag_check_duration_size_index(hls);
         if (ret < 0) {