lavfi: check av_strdup() return value

Signed-off-by: Paul B Mahol <onemda@gmail.com>
(cherry picked from commit 145a84717b)

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavfilter/af_join.c

@@ -214,6 +214,8 @@ static av_cold int join_init(AVFilterContext *ctx)
         snprintf(name, sizeof(name), "input%d", i);
         pad.type           = AVMEDIA_TYPE_AUDIO;
         pad.name           = av_strdup(name);
+        if (!pad.name)
+            return AVERROR(ENOMEM);
         pad.filter_frame   = filter_frame;
 
         pad.needs_fifo = 1;